Is a traveler permitted to complete (pray fully) the four-unit prayers during travel?
Chapter on the Traveler's Prayer
Al-Mughni
Book of Prayer
Primary text
The famous position attributed to Ahmad is that the traveler has the choice to either shorten the prayer to two units or complete it fully. This view is supported by the actions and statements of companions such as Uthman, Sa'd ibn Abi Waqqas, Ibn Mas'ud, Ibn Umar, and Aisha. It is also the position held by al-Awza'i, al-Shafi'i, and the well-known position of Malik. The primary evidence for choice is the verse: {There is no blame upon you if you shorten the prayer when you fear that those who disbelieve may put you to trial} [Quran 4:101], indicating concession which one may choose to take or leave, like other concessions. Furthermore, it is narrated that the Prophet (peace be upon him) sometimes shortened and sometimes completed the prayer, and this was accepted among the companions without censure.
Supporting text
A dissenting view held by Hammad ibn Abi Sulayman, and supported by al-Thawri and Abu Hanifa, is that the traveler is absolutely not permitted to complete the prayer; Hammad even mandated repetition (I'ada) for one who completed it. Another opinion states that if one sits for the duration of the Tashahhud after two units, the prayer is valid, otherwise it is invalid. Umar ibn Abd al-Aziz stated that two units in travel is mandatory and nothing else is correct. Some argue based on narrations that the foundation of the prayer was two units, and increasing beyond the obligatory minimum is not permissible, analogous to increasing upon Fajr prayer.