Musnad Ahmad 33:596

Ishaq ibn Isa narrated to us, Layth ibn Sa’d narrated to us, from Abu al-Zubayr, from Jabir ibn Abdullah, 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 initiated the fighting. If he was present during it, he would remain until it had passed."