Narrated Sulaiman bin Buraidah:
From his father who said: When the Messenger of Allah (sawS) sent a commander of an army, he would exhort him concerning himself to have Taqwa of Allah, and he would exhort him to be good to those who are with him among the Muslims. He would say: 'Fight in the Name of Allah, in the cause of Allah. Fight those who disbelieve in Allah, and do not steal from the spoils of war or be treacherous, nor mutilate, and do not kill a child. When you meet your enemy among the idolaters, then call them to one of the three options or choices, whichever of them they respond to then accept it from them, and refrain from them. Call them to Islam, and to relocate from their land to the land of Emigrants. Inform them that if they do that, then they will have similar to what those who emigrated have, and from them will be required similar to what is required from those who have emigrated. And if they refuse to relocate, then inform them that they will be like the Bedouins among the Muslim, and they will be treated the same as Bedouins are treated. There is no war spoils or Fay' for them, unless they fight along with the Muslims. If they refuse then seek aid from Allah against them and fight them. And if you lay siege to a fortress and they want you to grant them covenant from Allah and a covenant of His Prophet, then do not grant them the covenant of Allah nor the covenant of His Prophet. Rather grant them your own covenant and the covenant of your companions, it will be better than breaking Allah's covenant and the covenant of His Messenger. And if you lay siege to the people of a fortress and they want you to lift the siege for negotiating upon the judgement of Allah, then do not stop, but rather make them surrender to your judgement, for you do not know if you will come upon the judgement of Allah regarding them or not.' Or similar to that.
[Abu 'Eisa said:] There is something on this topic from An-Nu'man bin Muqarrin, and the Hadith of Buraidah is a Hasan Sahih Hadith