It was narrated that Abdullah bin Umar said:"A man stood up and said: 'O Messenger of Allah (ﷺ), how are the prayers at night to be done?' The Messenger of Allah (ﷺ) said: 'Prayers at night are (offered) two by two, then if you fear that dawn will come, pray witr with one.'"
أَخْبَرَنَا أَحْمَدُ بْنُ الْهَيْثَمِ، قَالَ حَدَّثَنَا حَرْمَلَةُ، قَالَ حَدَّثَنَا ابْنُ وَهْبٍ، قَالَ أَخْبَرَنِي عَمْرُو بْنُ الْحَارِثِ، أَنَّ ابْنَ شِهَابٍ، حَدَّثَهُ أَنَّ سَالِمَ بْنَ عَبْدِ اللَّهِ وَحُمَيْدَ بْنَ عَبْدِ الرَّحْمَنِ حَدَّثَاهُ عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، قَالَ قَامَ رَجُلٌ فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ صَلاَةُ اللَّيْلِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خِفْتَ الصُّبْحَ فَأَوْتِرْ بِوَاحِدَةٍ " .
Nesai
The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day • Hadith 1674