Yahya related to me from Malik from Abdullah ibn Dinar thatAbdullah ibn Umar used to say, "The maghrib prayer is the witr of thedaytime prayers."Malik said, "If someone prays witr at thebeginning of the night, and goes to sleep, and then wakes up and itseems good to him to pray, let him pray, two rakas at a time. That iswhat I like most of what I have heard."
App reference: Book 7, Hadith 22
USC-MSA web (English) reference: Book 7, Hadith 22
Arabic reference: Book 7, Hadith 276