Musnad Ahmad 5:202

'Abd al-Razzaq narrated to us, Israel informed us, from Abu Ishaq, from al-Harith, from Ali, who said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to perform the Witr prayer at the time of the Adhan, and he would perform the two rak'ahs of the Fajr prayer at the time of the Iqamah."