Section I: How Travellers Pray

Firstly: How to shorten prayers
Shortening prayers is the opposite of completing them, and it is to pray a four-unit prayer as two units.

Secondly: Shortening prayers when travelling
It is generally legislated to shorten four-unit prayers when travelling. [519] An exception is when a traveller prays behind a resident, in which case shortening prayers is not legislated. Consensus on this was related by Ibn al-Mundhir, Ibn `Abd al-Barr, Ibn Rushd, Ibn Qudamah, al-Nawawi, and Ibn Taymiyyah.

Thirdly: One who travels in order to take a dispensation
It is not permissible to travel for the purpose of taking dispensations when travelling, such as breaking the fast in Ramadan and shortening prayers. Whoever initiates travel for this purpose is not permitted to take dispensations. This is explicitly mentioned by Shafi`i and Hanbali jurists, and it is the position of choice of Ibn al-Qayyim and Ibn `Uthaymin.

Fourthly: Prayers that are not shortened
Shortening the fajr and maghrib prayers is not legislated. Consensus on this was related by Ibn al-Mundhir, Ibn Hazm, Ibn `Abd al-Barr, Ibn Battal, and al-Nawawi.

Fifthly: Ruling of shortening prayers
It is sunnah to shorten prayers when travelling. This is the position of the majority: the Malikis, Shafi`is, and Hanbalis. It is the position of most scholars of the Salaf and Khalaf.

Sixthly: Conditions for shortening prayers that the distance of travel be sufficient
How far one must travel to shorten prayers
Scholars hold various positions on how far one must travel in order to shorten prayers. The strongest positions are two:
The first position: The distance one must travel in order to shorten prayers is four bareeds (approximately 88 km). This is the position of the majority: the Malikis, Shafi`is, and Hanbalis. It is the position of some of the Salaf, Abu Yusuf the Hanafi, and is the position of the jurists among the Hadith masters. It is the position of choice of Ibn Baz.
The second position: Shortening prayers is valid in every journey, whether long or short, without a specific limit – as long as it is referred to as ‘travelling’. This is the position of the Zahiri school and some Hanbalis. It was chosen by Ibn Qudamah, Ibn Taymiyyah, Ibn al-Qayyim, al-Shawkani, al-Shinqiti, and Ibn `Uthaymin.
- Being unsure of the distance travelled:
Whoever doubts whether or not he has travelled a distance that permits shortening prayers does not shorten them. Rather, he is obligated to complete them. Hanbali jurists have explicitly mentioned this. It is also the apparent position of the Maliki school. Al-Shafi`i has explicitly mentioned this.
- Ruling of a wanderer with no particular destination:
A condition for shortening prayers is that one intend travelling a distance that permits it. If one is merely wandering about while lost or in search of a need without intending traveling a distance that permits shortening prayers, he may not shorten prayers. This is by agreement of the four schools of jurisprudence. 
- Not intending becoming a resident when travelling:
How long one may intend to stay in a locale before becoming a resident
Scholars have differed over the period of time which renders one a resident if he intends it. They did so according to many views, the strongest of which are three: [520] The cause of difference in the matter is what Ibn Rushd said: “It is an issue that has not been explicitly elucidated in Law.” Bidayat al-Mujtahid (169/1)
The first: A traveller does not shorten prayers if he intends staying in a locale for four or more days. [521] Hanbalis are of the position that if he intends residing in the same place for more than four days, his travels are interrupted. Ibn Taymiyyah is of the position that what matters when defining residency is `urf. This is the position of the Maliki [522] According to them, he does not count the day of arrival unless he arrived before dawn. As for the day of departure, if he intends to leave before sunset, there is no problem in not counting it. As for if his intention is to leave after sunset and before `isha’, then it appears that he would not count it in this case as well. and Shafi`i [523] However, they do not count the days of arrival and departure. schools, and one narration from Ahmad. [524] Ibn Taymiyyah took this as the position of choice out of precaution. It is the position of some of the Salaf out of caution.
The second: A traveller may shorten his prayers if he resides in a locale for nineteen days. If he increases upon that, he completes the prayers. This is the position of the Shafi`is, the chosen position of Ibn al-Mulaqqin, the spoken position of Ibn `Abbas, Ishaq ibn Rahawayh, and al-Tirmidhi.
The third: There is no specified time limit for shortening prayers so long as one does not intend residency or settling down. [525] Residency (iqamah) in a place is staying therein. Residency for the traveller is intending to remain in some locale for a period of time other than his own. Settling down (istitan) is when one has resolve to reside in a locale other than one’s own for a period of time. One’s settlement (watan) is any place one recites and settles in. This is the position Ibn Taymiyyah, Ibn al-Qayyim, Ibn Sa`di, and Ibn `Uthaymin.
- Waiting for a need to be fulfilled without intending residency:
Whoever waits for a need to be fulfilled without intending to become a resident may shorten prayers no matter how long he stays in that locale. This is by agreement between the four schools of jurisprudence.
- A navigator whose family is with him but does not intend residency:
A navigator [526] i.e. The captain of a ship. is a traveller and may shorten prayers even if his family is with him as long as he is not close to his homeland. This is the position of the majority: the Hanafis, Malikis, Shafi`is, and Dawud al-Zahiri.
- That the journey be permissible:
Scholars hold two positions regarding taking dispensations when travelling for an act of disobedience:
The first position: A condition of taking dispensations related to travelling – such as shortening prayers and breaking the fast in Ramadan – that the journey be permissible. If one travels for the purpose of disobedience, then it is not permissible to take dispensations. This is the position of the majority: the Malikis, Shafi`is, and Hanbalis.
The second position: Every traveller may take the dispensations related to travel regardless of whether the journey is permissible or an act of disobedience. This is the position of the Hanafi school, one narration from Malik, and a group of the Salaf. It is the position of choice of Ibn Hazm, Ibn Taymiyyah, al-Shawkani, al-Sa`di, and Ibn Baz. It is supported by Ibn `Uthaymin. 
- Leaving one’s homeland:
It is a condition for shortening prayers that one have left the residences of his homeland, departed from its buildings, and left them behind him. [527] It is permissible to act upon the dispensations granted to travellers in the airport if it is outside of city limits. As for if the airport is within city limits, then this is not permissible until the plane takes off and is departs from the city’s urban developments. This is by agreement of the four schools of jurisprudence.

Seventhly: Prayer time entering during travel
It is not a condition for shortening prayers that the prayer time begin after one begins his travels. One who travels after a prayer time has entered may shorten prayers. This is the position of the majority: the Hanafis, Malikis, Shafi`is, and one narration from Ahmad.

Eighthly: Starting the prayer as a resident and completing it as a traveller
One who starts the prayer as a resident and then travels must offer the prayer to completion. Consensus on this was related by al-Mawardi and al-Nawawi.

Ninthly: Starting the prayer as a traveller and completing it as a resident
One who starts the prayer as a traveller and then becomes a resident must offer the prayer as a resident. [528] An example of this is when one starts praying on a ship in one locale, then the ship embarks and leaves that locale behind while one is praying. Similarly, if one starts prayer in a plane as a resident and then the plane takes off while he is praying. This is explicitly mentioned by Hanafi, Shafi`i, and Hanbali jurists.

Tenthly: Intending shortening prayers
Scholars are of two positions regarding whether intending shortening the prayer is a condition:
The first position: Intending shortening the prayer during the opening Allahu Akbar is a condition for the permissibility of shortening it. This is the position of the Shafi`i and Hanbali schools, one of two positions of the Malikis, [529] This condition on the intention of shortening prayers, according to this position, is for the first prayer shortened. and the majority of jurists.
The second position: Shortening prayers does not require an intention. This is the position of the Hanafis, [530] This is because it is fard according to them to shorten prayers when travelling. In reality, it is not shortening prayers, but completing them. one of two positions among Malikis, a narration from Ahmad, and the position of choice of Ibn Taymiyyah and Ibn `Uthaymin.

Eleventhly: Making up prayers missed while travelling as a resident, and vice versa making up a prayer missed as a resident while travelling
Whoever misses a prayer as a resident makes it up in completion when travelling. Making up a prayer missed as a traveller while residing
Scholars are of two positions regarding one who misses a prayer while travelling and makes it up while residing:
The first position: One who misses a prayer when travelling makes it up as a shortened prayer when residing. This is the position of the Hanafi and Maliki schools, al-Shafi`i’s old position, the position of Sufyan al-Thawri, and the position of choice of Ibn `Uthaymin.
The second position: One who misses a prayer when travelling makes it up as a complete prayer when residing. This is the soundest position of the Shafi`i school and the position of the Hanbali school and Dawud al-Zahiri. It is the position of choice of Ibn Baz.

Twelfthly: A traveller praying behind a resident imam
If a traveller prays behind a resident imam, he offers the prayer to completion. This is by agreement of the four schools of jurisprudence. [531] There is a difference of opinion among Malikis. Does he have to repeat his prayer after completing it behind a resident?

Thirteenthly: A traveller praying behind an imam who might be a resident or a traveller
Scholars hold two positions regarding a traveller praying behind an imam who be a resident or a traveller:
The first position: If a traveller prays behind an imam who might be a traveller or a resident, he is obliged to offer his prayer to completion. This is the position of the Shafi`i and Hanbali schools.
The second position: He completes his prayer if the imam does so, but if the imam shortens his prayer, then the follower is not obliged to complete his prayer. This is one position according to Shafi`is and was chosen by Ibn `Uthaymin.

Fourteenthly: Optional prayers when travelling unconditional optional prayers when travelling
Offering unconditional optional prayers when travelling is legislated. Consensus on this was related by al-Nawawi and Ibn Muflih. 
- The two units before fajr and witr when travelling:
The two units of sunnah prayer before fajr and the witr prayer are offered when travelling. This is by agreement of the four schools of jurisprudence. 
- Other rawatib sunnahs when travelling:
It is not sunnah to offer other rawatib sunnah prayers when travelling, other than the two units before fajr and the witr prayer. Many Hanafi sheikhs hold this position. It is the position of choice of Ibn Taymiyyah, Ibn al-Qayyim, and Ibn `Uthaymin. The Permanent Council issued its verdict according to this position. 
- Offering the witr prayer while riding during travel:
It is permissible to offer the witr prayer while riding during travel. This is the position of the majority: the Malikis, Shafi`is, Hanbalis, Dawud, and the majority of scholars from the Companions and those after them. 
- Facing the qiblah when offering optional prayers while riding during travel:
This has been covered in the section on offering additional prayers when travelling.