Sayyiduna Uqbah bin Amir (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) asked Sayyiduna Abu Bakr (may Allah be pleased with him): When do you perform the witr? He replied: I keep praying two rak'ahs at a time, then I perform the witr before I sleep. The Prophet (peace and blessings be upon him) said to him: This is the way of a cautious believer. He asked Sayyiduna Umar (may Allah be pleased with him): When do you perform the witr? He replied: I keep praying two rak'ahs at a time, then I sleep, until I perform the witr in the last part of the night (after waking up). The Prophet (peace and blessings be upon him) said: This is the way of a strong believer.
Imam al-Tabarani recorded this narration in al-Mu'jam al-Kabir; its chain contains a narrator, Ibn Lahi'ah, about whom criticism has been made.