Musnad Ahmad 1153:2380

Hassan narrated to us, he said: Hammad ibn Salamah narrated to us, from Hisham ibn Urwah, from his father, from Aisha, that when the Messenger of Allah (peace and blessings of Allah be upon him) finished with the Confederates (al-Ahzab), he entered the bathing place to bathe. Gabriel came, and I saw him through the gap in the door, his head covered in dust. He said: "O Muhammad, have you laid down your weapons?" He (the Prophet) said: "We have not laid down our weapons yet. Proceed to Banu Qurayza."