Musnad Abu Ya'la al-Mawsili 117:32

Ibrahim ibn al-Hajjaj narrated to us, Hammad narrated to us, from Thabit, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) delayed the Isha prayer one night until half of the night had passed. Then he came out and led them in prayer, and he did not mention ablution.