ENOfficial
It was narrated that Ibn Umar said: "I heard the Messenger of Allah (ﷺ) on the minbar, when he was asked about prayers at night, say: "Two by two, then if you fear that dawn will come, pray witr with one rak'ah.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ ابْنِ أَبِي لَبِيدٍ، عَنْ أَبِي سَلَمَةَ، عَنِ ابْنِ عُمَرَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى الْمِنْبَرِ يُسْأَلُ عَنْ صَلاَةِ اللَّيْلِ فَقَالَ " مَثْنَى مَثْنَى فَإِذَا خِفْتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ " .
sunnah.com