Hadith 18:4
Sahih (Darussalam)
It was narrated that Ibn Abbas said:
"Allah (SWT) enjoined the prayer on the tongue of your Prophet (ﷺ): four (rak'ahs) while a resident, two rak'ahs while traveling, and one rak'ah during times of fear."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ بُكَيْرِ بْنِ الأَخْنَسِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ فَرَضَ اللَّهُ الصَّلاَةَ عَلَى لِسَانِ نَبِيِّكُمْ صلى الله عليه وسلم فِي الْحَضَرِ أَرْبَعًا وَفِي السَّفَرِ رَكْعَتَيْنِ وَفِي الْخَوْفِ رَكْعَةً
Original Reference: Sunan an-Nasa'i 1532