The Book of Salah
5/3. Chapter:
How The Salah Was Made Obligatory
Sunan an-Nasai
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، وَعَبْدُ الرَّحْمَنِ، قَالاَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ بُكَيْرِ بْنِ الأَخْنَسِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ فُرِضَتِ الصَّلاَةُ عَلَى لِسَانِ النَّبِيِّ صلى الله عليه وسلم فِي الْحَضَرِ أَرْبَعًا وَفِي السَّفَرِ رَكْعَتَيْنِ وَفِي الْخَوْفِ رَكْعَةً .
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."
Reference : Sunan an-Nasa'i 456In-book reference : Book 5, Hadith 9English translation : Vol. 1, Book 5, Hadith 457