Musnad Abu Ya'la al-Mawsili 44:1

Abu Ya'la informed us, he said: It was read to Bishr ibn al-Walid, from Abu Yusuf, from Abu Hanifah, from Alqamah ibn Marthad, from Ibn Buraydah, from his father, from the Prophet (peace be upon him), that when he would send out a raiding party or an army, he would advise its commander to fear Allah regarding his own self in particular, and he would advise him regarding those who were with him from the Muslims to treat them well. Then he would say: "Fight in the name of Allah. Fight those who disbelieve in Allah. Do not act treacherously, do not break your pledges, do not mutilate, and do not kill a newborn child. When you meet your enemy from the polytheists, invite them to Islam; if they accept, then accept it from them and refrain from them. Then invite them to move from their land to the land of the Muslims. If they do so, then accept it from them. Otherwise, inform them that they will be like the Bedouin Muslims; the ruling of Allah that applies to the Muslims will apply to them, and they will have no share in the fay' (spoils taken without fighting) or the ghanimah (spoils of war). If they refuse that, then invite them to pay the jizyah. If they do so, then accept it from them and refrain from them. If you besiege a fortress or a city, and they want you to bring them down upon the judgment of Allah, do not bring them down upon it, for you do not know what the judgment of Allah is. Rather, bring them down upon your own judgment, then judge regarding them as you see fit. If you besiege a castle, do not grant them the covenant of Allah or the covenant of His Messenger, but grant them your own covenants and the covenants of your fathers, for it is easier for you to break your own covenants and the covenants of your fathers [than to break the covenant of Allah and His Messenger]."