Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
bukhari:993Yaḥyá b. Sulaymān > Ibn Wahb > ʿAmr > ʿAbd al-Raḥman b. al-Qāsim from his father > ʿAbdullāh b. ʿUmar

The Prophet ﷺ said, "Night prayer is offered as two rakʿat followed by two rakʿat and so on, and if you want to finish it, pray only one rakʿa which will be witr for all the previous rakʿat." Al-Qasim said, "Since we attained the age of puberty we have seen some people offering a three-rakʿat prayer as witr and all that is permissible. I hope there will be no harm in it."  

البخاري:٩٩٣حَدَّثَنَا يَحْيَى بْنُ سُلَيْمَانَ قَالَ حَدَّثَنِي ابْنُ وَهْبٍ قَالَ أَخْبَرَنِي عَمْرٌو أَنَّ عَبْدَ الرَّحْمَنِ بْنَ الْقَاسِمِ حَدَّثَهُ عَنْ أَبِيهِ عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ قَالَ

قَالَ النَّبِيُّ ﷺ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا أَرَدْتَ أَنْ تَنْصَرِفَ فَارْكَعْ رَكْعَةً تُوتِرُ لَكَ مَا صَلَّيْتَ قَالَ الْقَاسِمُ وَرَأَيْنَا أُنَاسًا مُنْذُ أَدْرَكْنَا يُوتِرُونَ بِثَلاَثٍ وَإِنَّ كُلاًّ لَوَاسِعٌ أَرْجُو أَنْ لاَ يَكُونَ بِشَىْءٍ مِنْهُ بَأْسٌ  


See similar narrations below:

Collected by Nasāʾī's Kubrá
nasai-kubra:444al-Rabīʿ b. Sulaymān > Ḥajjāj b. Ibrāhīm > Ibn Wahb > ʿAmr b. al-Ḥārith > ʿAbd al-Raḥman Wahū Ibn al-Qāsim from his father > ʿAbdullāh b. ʿUmar

The Messenger of Allah ﷺ said: "Prayer at night is two by two, then when you want to finish, pray one rak'h which will make the total number that you prayed odd." (Using translation from Nasāʾī 1692)   

الكبرى للنسائي:٤٤٤أَخْبَرَنِي الرَّبِيعُ بْنُ سُلَيْمَانَ قَالَ حَدَّثَنَا حَجَّاجُ بْنُ إِبْرَاهِيمَ قَالَ حَدَّثَنَا ابْنُ وَهْبٍ عَنْ عَمْرِو بْنِ الْحَارِثِ عَنْ عَبْدِ الرَّحْمَنِ وَهُوَ ابْنُ الْقَاسِمِ حَدَّثَهُ عَنْ أَبِيهِ عَنْ عَبْدِ اللهِ بْنِ عُمَرَ

عَنْ رَسُولِ اللهِ ﷺ قَالَ «صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا أَرَدْتَ أَنْ تَنْصَرِفَ فَارْكَعْ رَكْعَةً وَاحِدَةً تُوتِرُ لَكَ مَا صَلَّيْتَ»