Sunan An-Nasa'i - سنن النسائي
20. The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day - كتاب قيام الليل وتطوع النهار
26) Chapter: How to pray at night
It was narrated that Tawus said:
"Ibn Umar said: "A man asked the Messenger of Allah (ﷺ) about prayer at night. He said: "Two by two, and if you fear that dawn will come, then one.'"
26) باب كَيْفَ صَلاَةُ اللَّيْلِ
أَخْبَرَنَا مُحَمَّدُ بْنُ قُدَامَةَ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ حَبِيبٍ، عَنْ طَاوُسٍ، قَالَ قَالَ ابْنُ عُمَرَ سَأَلَ رَجُلٌ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ صَلاَةِ اللَّيْلِ فَقَالَ . " مَثْنَى مَثْنَى فَإِذَا خَشِيتَ الصُّبْحَ فَوَاحِدَةٌ "