Musnad Ahmad 33:1124

Ishaq ibn Isa narrated to us, Sharik narrated to us, from Abdullah ibn Muhammad ibn Aqil, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have been commanded to fight the people until they say: 'There is no god but Allah.' If they say it, they have protected their blood and their wealth from me, except by its right, and their reckoning is with Allah."