Sunan Abi Dawud 1247
سنن أبي داود#1247Sahihحَدَّثَنَا مُسَدَّدٌ، وَسَعِيدُ بْنُ مَنْصُورٍ، قَالاَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ بُكَيْرِ بْنِ الأَخْنَسِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ فَرَضَ اللَّهُ تَعَالَى الصَّلاَةَ عَلَى لِسَانِ نَبِيِّكُمْ صلى الله عليه وسلم فِي الْحَضَرِ أَرْبَعًا وَفِي السَّفَرِ رَكْعَتَيْنِ وَفِي الْخَوْفِ رَكْعَةً .
Narrated Ibn 'Abbas:Allah, the Exalted, prescribed prayer for you, through the tongue of your Prophet (ﷺ), four rak'ahs while resident, two rak'ahs while travelling and one rak'ah in time of danger
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: 4:50