Musnad Ahmad 811:2

'Abd al-Samad narrated to us, Abu Hilal narrated to us, 'Abd Allah ibn Sawadah al-Qushayri informed us, from Anas ibn Malik—one of the Banu Ka'b, brother of the Banu Qushayr—who said: The cavalry of the Messenger of Allah (may Allah bless him and grant him peace) raided us. I set out to the Messenger of Allah (may Allah bless him and grant him peace) and reached him while he was eating. He said to me: "Draw near and eat." I said: "I am fasting." Then he mentioned the rest of the hadith.