Muwatta Malik Book 7, Hadith 24
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.
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 Hisham ibn Urwa from his father that Abdullah ibn Masud said, "I do not mind if the iqama for the subh prayer is called while I am still praying witr."