He heard the Messenger of Allah ﷺ say: "Prayer at night is two rak'ahs by two rak'ahs, then when you fear tat dawn will break, pray witr with one rak'ah." (Using translation from Nasāʾī 1695)
أَخْبَرَهُ أَنَّ رَسُولَ اللهِ ﷺ قَالَ صَلَاةُ اللَّيْلِ رَكْعَتَانِ فَإِذَا خِفْتُمُ الصُّبْحَ فَأَوْتِرُوا بِوَاحِدَةٍ