Musnad Ahmad 33:420

'Abd al-Samad and Mu'awiyah ibn 'Amr narrated to us, they said: Za'idah narrated to us, 'Abdullah ibn Muhammad ibn 'Aqil narrated to us, from Jabir ibn 'Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to Abu Bakr: "At what time do you perform the Witr prayer?" He said: "At the beginning of the night, after the 'Isha prayer." He said: "And you, O 'Umar?" He said: "At the end of the night." The Messenger of Allah (peace and blessings of Allah be upon him) then said: "As for you, O Abu Bakr, you have taken the more reliable course; and as for you, O 'Umar, you have taken the course of strength."