´It was narrated that 'Aishah said:` "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."
Hadith Referenceسنن نسائي / كتاب الصلاة / 454
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:متفق عليه
´Abu 'Amr - meaning, Al-Awza'i - said that he asked Az-Zuhri about the prayer of the Messenger of Allah (ﷺ) in Makkah before the Hijrah to Al-Madinah. He said:` "Urwah told me that 'Aishah said: 'Allah enjoined the salah upon the Messenger of Allah (ﷺ), and the first thing that He enjoined was two Rak'ahs at a time, then it was made complete four Rak'ahs while in the state of residence but the prayer when traveling remained two Rak'ahs, as it was first enjoined.'"
Hadith Referenceسنن نسائي / كتاب الصلاة / 455
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده صحيح
´It was narrated that 'Aishah said:` "The Salah was enjoined two Rak'ahs at a time, then the Salah when traveling remained like that, but the Salah while resident was increased."
Hadith Referenceسنن نسائي / كتاب الصلاة / 456
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:متفق عليه
Hadith Takhrij«صحیح البخاری/الصلاة 1 (350)، صحیح مسلم/صلاة المسافرین1 (685)، سنن ابی داود/الصلاة 270 (1198)، (تحفة الأشراف: 16348)، موطا امام مالک/قصر الصلاة 2 (8)، مسند احمد 6/272 (صحیح)»
´It was narrated that Ibn 'Abbas said:` "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."
Hadith Referenceسنن نسائي / كتاب الصلاة / 457
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم
´It was narrated that Umayyah bin 'Abdullah bin Khalid bin Asid said to Ibn 'Umar:` "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?" [1] 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." [1] An-Nisa' 4:101.
Hadith Referenceسنن نسائي / كتاب الصلاة / 458
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده حسن
Hadith Takhrij«سنن ابن ماجہ/إقامة 73 (1066)، مسند احمد 2/94، 148، ویأتي عند المؤلف (برقم: 1435) (صحیح)»