Muwatta Malik Book 7, Hadith 19
Yahya related to me from Malik that Nafi said, "I was with
Abdullah ibn Umar in Makka. The sky was clouded over and Abdullah
feared that dawn was approaching so he prayed one raka for witr. Then
the clouds cleared and he saw that it was still night, so he made his
prayers even with one raka. Then he continued to pray two rakas at a
time, until when he feared the approach of dawn, he prayed one raka
for witr."
Yahya related to me from Malik that he had heard that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, used to say, "If someone fears that he will sleep through till the morning, let him pray the witr before he sleeps, and if some one hopes to wake for the last part of the night, let him delay his witr."
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say the taslim between the two rakas and the one raka of witr so that he could order something he needed.