Sunan an Nasai
1695
Sahih+2

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

SahihAbu Ghuddah
SahihAl-Albani