Sunan an-Nasa'i 453
سنن النسائي#453Sahihأَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، قَالَتْ أَوَّلَ مَا فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَأُتِمَّتْ صَلاَةُ الْحَضَرِ .
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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 5:6