Musnad Abu Ya'la al-Mawsili 150:22

Ishaq narrated to us, Hassan bin Ibrahim narrated to us, Hisham bin Urwah narrated to us, from his father, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to pray between the Isha [prayer] thirteen rak'ahs, performing witr from them with five, in which he would perform the taslim only in the fifth.