Sunan an-Nasa'i · Hadith 1671
The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day - كتاب قيام الليل وتطوع النهار
أخبرنا قتيبة، قال حدثنا الليث، عن نافع، عن ابن عمر، عن النبي صلى الله عليه وسلم قال " صلاة الليل مثنى مثنى فإذا خفت الصبح فأوتر بواحدة " .
It was narrated from Ibn Umar that: The Prophet (ﷺ) said: "prayers at night are (offered) two by two, then if you fear that dawn will come, pray witr with one."
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).