" صَلاَةُ اللَّيْلِ رَكْعَتَيْنِ رَكْعَتَيْنِ فَإِذَا خِفْتُمُ الصُّبْحَ فَأَوْتِرُوا بِوَاحِدَةٍ "
It was narrated from Ibn 'Umar that: 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."