Qutayba bin Sa'id bin Jamil قتيبة بن سعيد بن جميل · The Book of Salah

"The first time the Salah was enjoined it was two Rak'ahs, and it remained as such when traveling, but the Salah while resident was made complete."

"The Salah was enjoined on the lips of the Prophet (ﷺ), four Rak'ahs while resident, and two while traveling, and one Rak'ah during times of fear."

"How can the Salah be shortened as Allah says: There is no sin on you if you shorten As-Salah (the prayer) if you are in fear?" Ibn 'Umar said: "O son of my brother! The Messenger of Allah (ﷺ) came to us when we had gone astray and he taught us. One of the things that he taught us was that Allah, the Mighty and Sublime, has commanded us to pray two Rak'ahs when traveling." An-Nisa' 4:101.

"A man asked the Messenger of Allah (ﷺ): 'O Messenger of Allah, how many prayers has Allah enjoined upon His slaves?' He said: 'Allah has enjoined upon His slaves (five) prayers.' He said: 'O Messenger of Allah, is there anything before them or after them?' He said: 'Allah has enjoined upon His salves (five) prayers.' The man swore that he would not do anything more or less than that. The Messenger of Allah (ﷺ) said: 'If he is speaking the…

"We were with the Messenger of Allah (ﷺ) and he said: 'Will you not pledge to the Messenger of Allah (ﷺ)?' And he repeated it three times. So we stretched forth our hands to give our pledge. We said: 'O Messenger of Allah, we are willing to give you our pledge, but on what?' He said: 'That you will worship Allah and not associate anything with him, and (offer) the five daily prayers.' And he said, very quietly: 'And you…

"The first thing for which a person will be brought to account will be his Salah. If it is complete (all well and good), otherwise Allah will say: 'Look and see if My slave did any voluntary prayer.' If he is found to have done voluntary prayers, his obligatory prayers will be completed therewith."

"I heard Abu Juhaifah say: 'The Messenger of Allah (ﷺ) set off at midday, during the time of intense heat' - (One of the narrators) Ibn Al-Muthanna said, to Al-Batha' - and he performed Wudu', and prayed Zuhr, two Rak'ahs, and 'Asr, two Rak'ahs, with a short spear ('Anzah) in front of him.

"We used to estimate how long the Messenger of Allah (ﷺ) stood when praying in Zuhr and 'Asr. We estimated that he stood in Zuhr for as long as it take to recite thirty verses, as long as Surat As-Sajadah in the fits two Rak'ahs, and half that in the last two. And we estimated that he stood for as long in the fits two Rak'ahs, and half that in the last two. And we estimated that he stood for…

"Sa'eed bin Jubair led us in prayer in Jam'. (He prayed) Maghrib, three Rak'ahs with an Iqamah, then he prayed 'Isha', two Rak'ahs. Then he mentioned that 'Abdullah bin 'Umar had done that, and he mentioned that the Messenger of Allah (ﷺ) had done that."

"The Messenger of Allah (ﷺ) used to pray voluntary prayers (Usabbih) while riding his mount, facing whatever direction it was facing, and he would pray Witr likewise, but he would not offer the prescribed prayers on it."

"The Messenger of Allah (ﷺ) used to pray while on his animal when he was coming back from Makkah to Madinah. Concerning this, the verse was revealed: So wherever you turn (yourselves or your faces) there is the Face of Allah.'" Al-Baqarah 2:115.