Sunan an-Nasa'i 1442
سنن النسائي#1442Sahihأَخْبَرَنَا يَعْقُوبُ بْنُ مَاهَانَ، قَالَ حَدَّثَنَا الْقَاسِمُ بْنُ مَالِكٍ، عَنْ أَيُّوبَ بْنِ عَائِذٍ، عَنْ بُكَيْرِ بْنِ الأَخْنَسِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ إِنَّ اللَّهَ عَزَّ وَجَلَّ فَرَضَ الصَّلاَةَ عَلَى لِسَانِ نَبِيِّكُمْ صلى الله عليه وسلم فِي الْحَضَرِ أَرْبَعًا وَفِي السَّفَرِ رَكْعَتَيْنِ وَفِي الْخَوْفِ رَكْعَةً .
It was narrated that Ibn 'Abbas said:"Allah, the Mighty and Sublime, enjoined the prayer on the tongue of your Prophet (ﷺ): While a resident four (rak'ahs), while traveling two, and at times of fear one
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:
In-book reference: 15:10