Narrated An-Numan ibn Bashir: I am the one who is best informed of the time of this prayer, i. e. the night prayer. The Messenger of Allah ﷺ used to offer it at the hour when the moon went down on its third night.
Hadith Referenceسنن ابي داود / كتاب الصلاة / 419
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده صحيح, مشكوة المصابيح (613)