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.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
muslim:749b – Abū Bakr b. Abū Shaybah And ʿAmrw al-Nāqid Wazuhayr b. Ḥarb > Zuhayr > Sufyān b. ʿUyaynah > al-Zuhrī > Sālim from his father

It consists of pairs of rak'ahs, but if one fears morning is near, he should make it an odd number by praying one rak'ah.  

مسلم:٧٤٩b – حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ وَعَمْرٌو النَّاقِدُ وَزُهَيْرُ بْنُ حَرْبٍ قَالَ زُهَيْرٌ حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ عَنِ الزُّهْرِيِّ عَنْ سَالِمٍ عَنْ أَبِيهِ

سَمِعَ النَّبِيَّ ﷺ يَقُولُ ح وَحَدَّثَنَا مُحَمَّدُ بْنُ عَبَّادٍ وَاللَّفْظُ لَهُ حَدَّثَنَا سُفْيَانُ حَدَّثَنَا عَمْرٌو عَنْ طَاوُسٍ عَنِ ابْنِ عُمَرَ ح وَحَدَّثَنَا الزُّهْرِيُّ عَنْ سَالِمٍ عَنْ أَبِيهِ أَنَّ رَجُلاً سَأَلَ النَّبِيَّ ﷺ عَنْ صَلاَةِ اللَّيْلِ فَقَالَ مَثْنَى مَثْنَى فَإِذَا خَشِيتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ  

See similar narrations below:

Collected by Bayhaqī
bayhaqi:4766 – Abū ʿAbdullāh al-Ḥāfiẓ > Abū ʿAbdullāh Muḥammad b. Yaʿqūb > al-Ḥusayn b. Muḥammad b. Ziyād > Muḥammad b. ʿAbbād al-Makkī > Sufyān > al-Zuhrī > Sālim from his father > ʿAmr > Ṭāwus > Ibn ʿUmar

[Machine] That a man asked the Prophet ﷺ about the night prayer, so he said: "Pray two by two. When you fear the break of dawn, perform the Witr prayer with one rak'ah."  

البيهقي:٤٧٦٦ – وَأَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ ثنا أَبُو عَبْدِ اللهِ مُحَمَّدُ بْنُ يَعْقُوبَ ثنا الْحُسَيْنُ بْنُ مُحَمَّدِ بْنِ زِيَادٍ ثنا مُحَمَّدُ بْنُ عَبَّادٍ الْمَكِّيُّ ثنا سُفْيَانُ ثنا الزُّهْرِيُّ عَنْ سَالِمٍ عَنْ أَبِيهِ قَالَ وَحَدَّثَنَا عَمْرٌو عَنْ طَاوُسٍ عَنِ ابْنِ عُمَرَ

أَنَّ رَجُلًا سَأَلَ النَّبِيَّ ﷺ عَنْ صَلَاةِ اللَّيْلِ فَقَالَ مَثْنَى مَثْنَى فَإِذَا خَشِيتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ  

رَوَاهُ مُسْلِمٌ فِي الصَّحِيحِ عَنْ مُحَمَّدِ بْنِ عَبَّادٍ الْمَكِّيِّ