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 ‏"‏ ‏.‏

It was narrated that Tawus said: "Ibn Umar said: "A man asked the Messenger of Allah (PBUH) about prayer at night. He said: "Two by two, and if you fear that dawn will come, then one.'" Translation Not Available

Book Ref: Sunan An Nisai Book 20 Hadith 1667
Web Ref:  Sunan An Nisai Vol 2 Book 20 Hadith 1668