Yahya related to me from Malik from Yahya ibn Said that Said ibnal-Musayyab said, "Abu Bakr as-Siddiq used to pray witr when he wishedto go to bed, and Umar ibn al-Khattab used to pray witr at the end ofthe night. As for me, I pray witr when I go to bed."
App reference: Book 7, Hadith 16
USC-MSA web (English) reference: Book 7, Hadith 16
Arabic reference: Book 7, Hadith 270