Musnad Ahmad 1017:95

'Abd al-Rahman narrated to us, Sufyan narrated to us, from 'Alqamah ibn Marthad, from Sulayman ibn Buraydah, from his father, who said: When the Messenger of Allah (ﷺ) would appoint a commander over an army or a detachment, he would advise him specifically to fear Allah, and to treat the Muslims who were with him well. Then he would say: "Fight in the name of Allah, in the path of Allah. Fight those who disbelieve in Allah. Fight, but do not exceed the limits, do not commit treachery, do not mutilate, and do not kill a newborn child. When you meet your enemy from among the polytheists, invite them to one of three options (or qualities). Whichever one they respond to, accept it from them and refrain from them. Invite them to Islam; if they respond to it, accept it from them and refrain from them. Then invite them to move from their land to the land of the Emigrants (Muhajirin), and inform them that if they do so, they shall have what the Emigrants have, and upon them shall be what is upon the Emigrants. If they refuse to move from it, inform them that they will be like the Bedouin Muslims; the ruling of Allah that applies to the Muslims applies to them, but they shall have no share in the spoils of war or the fay' (booty taken without fighting) unless they strive (jihad) alongside the Muslims. If they refuse, then ask them for the jizyah (tribute). If they respond to you, accept it from them and refrain from them. If they refuse, then seek the help of Allah and fight them. When you besiege the people of a fortress and they want you to grant them the covenant of Allah and the covenant of His Prophet, do not grant them the covenant of Allah nor the covenant of His Prophet. Rather, grant them your own covenant, the covenant of your father, and the covenants of your companions; for if you break your own covenants and the covenants of your fathers, it is easier than breaking the covenant of Allah and the covenant of His Messenger. And if you besiege the people of a fortress and they want you to let them down based on the judgment of Allah, do not let them down based on the judgment of Allah. Rather, let them down based on your own judgment; for you do not know whether you will hit the judgment of Allah regarding them or not." 'Abd al-Rahman said: This or something similar to it.