Musnad Ahmad 33:468

Hujayn ibn al-Muthanna Abu Umar narrated to us, Layth narrated to us, from Abu al-Zubayr, from Jabir, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) would not conduct a military expedition during the sacred month, unless he was attacked—or they attacked. If that [month] arrived, he would remain until it had passed."