Muwatta Malik Book 7, Hadith 23
Yahya related to me from Malik from Abd al Karim ibn
Abi'l-Mukhariq al-Basri from Said ibn Jubayr that Abdullah ibn Abbas
slept, and when he woke up, he said to his servant, "Go and see what
the people have done," (by that time his sight had gone.) The servant
went out and returned saying, "The people have left from subh," so
Abdullah ibn Abbas got up and prayed witr and then prayed subh.
Yahya related to me from Malik from Abdullah ibn Dinar that Abdullah ibn Umar used to say, "The maghrib prayer is the witr of the daytime prayers."
Malik said, "If someone prays witr at the beginning of the night, and goes to sleep, and then wakes up and it seems good to him to pray, let him pray, two rakas at a time. That is what I like most of what I have heard."
Yahya related to me from Malik that he had heard that Abdullah ibn Abbas and Ubada ibn as-Samit and al-Qasim ibn Muhammad and Abdullah ibn Amir ibn Rabia had all prayed witr after the break of dawn.