AbuMijlaz narrated that Ibn 'Umar said:
"The Messenger of Allah(ﷺ) said: 'Night prayers are to be offered two by two, and Witrisone Rak'ah.' I said: 'What do you think if I become drowsyand I wantto sleep?' He said: 'Put "what do you think" upthere with that star?(i.e., don't think about it at all).' Iraised my head and saw As-Simak.* He repeated that the Messenger ofAllah (ﷺ) said, 'Nightprayers are to be offered two by two, andWitr is one Rak'ah, beforedawn.'"
English reference: Vol. 1, Book 5, Hadith 1175
Arabic reference: Book 5, Hadith 1231