Nafi' said, “I was with Ibn ‘Umar in Mecca when the sky was cloudy and he was afraid the morning might have come, so he observed a witr with one rak'a. The sky then cleared and he saw that it was still night, so he made it a pair by praying one rak'a; then he prayed series of two rak'as, and when he was afraid morning was near he observed a witr with one.”
‘Ali said that God’s Messenger used to pray three rak'as when observing the witr, reciting nine suras from al-Mufassal in the course of them, three in each rak'a, the last of them being “Say, He is God, One” (Al-Qur’an; 112).
‘A’isha said that God’s Messenger used to pray sitting, and would recite the Qur’an while sitting; then when about thirty or forty verses of his recitation remained he stood up and recited while standing. Then he bowed, then he prostrated himself, and after that he did the same kind of thing in the second rak'a.
Malik said he heard that a man asked Ibn ‘Umar whether the witr was obligatory, and ‘Abdallah said, “God’s Messenger observed the witr and the Muslims observed the witr.” The man kept repeating his question and ‘Abdallah kept saying, “God’s Messenger observed the witr and the Muslims observed the witr.”