Maliks Muwatta Book 7, Hadith Number 22.

Section : The Command to Pray the Witr.

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.”