Muwatta Malik Book 7, Hadith 20
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.
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 from Ibn Shihab that Sad ibn Abi Waqqas used to pray witr after isha with one raka.
Malik said, "This is not the situation with us. Rather three is the minimum for witr."