The night prayer consists of pairs and when you see the approach of dawn, make this number odd by one rak'ah. It was said to Ibn 'Umar: What does the (word) pair imply? He said: (It means) that salutation is uttered after every two rak'ahs.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا رَأَيْتَ أَنَّ الصُّبْحَ يُدْرِكُكَ فَأَوْتِرْ بِوَاحِدَةٍ فَقِيلَ لاِبْنِ عُمَرَ مَا مَثْنَى مَثْنَى قَالَ أَنْ يُسَلِّمَ فِي كُلِّ رَكْعَتَيْنِ  

[Machine] The Messenger of Allah ﷺ said, "The night prayer is (to be performed in) pairs, pairs. But if you fear the coming of dawn, then perform one rakaah (unit of prayer) for witr." I asked, "What is (meant by) pairs, pairs?" He said, "Two rakaahs, two rakaahs."  

قَالَ رَسُولُ اللهِ ﷺ صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِنْ خَشِيتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ قَالَ قُلْتُ مَا مَثْنَى مَثْنَى؟ قَالَ رَكْعَتَانِ رَكْعَتَانِ  

[Machine] The Messenger of Allah ﷺ said, "The night prayer should be performed in sets of two. When you see that dawn is approaching, then conclude with one unit of prayer." A man asked Ibn Umar, "What does 'sets of two' mean?" He replied, "You make Salaam after every two units of prayer."  

قَالَ رَسُولُ اللهِ ﷺ صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا رَأَيْتَ أَنَّ الصُّبْحَ مُدْرِكُكَ فَأَوْتِرْ بِرَكْعَةٍ فَقَالَ رَجُلٌ لِابْنِ عُمَرَ مَا مَثْنَى؟ قَالَ تُسَلِّمُ فِي كُلِّ رَكْعَتَيْنِ  

"عَنْ عُقْبَةَ بْنِ حُرَيْث قَالَ: سَمِعْتُ ابْنَ عُمَرَ يُحَدِّثُ أن رَسُولَ الله ﷺ قَالَ: صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى، فَإذَا رأَيْتَ الصُّبْحَ يُدْرِكُكَ فَأوْتِرْ بِوَاحِدَةٍ، فَقِيلَ لابنِ عُمَرَ: مَا مَثْنَى مَثْنَى؟ قالَ: تُسَلِّمُ فِى كُلِّ رَكْعَتَيْنِ".