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." (AR)
App reference (AR): Book 7, Hadith 16 (AR)
USC-MSA web (English) reference: Book 7, Hadith 16 (AR)
Arabic reference (AR): Book 7, Hadith 270 (AR)