Musannaf Ibn Abi Shayba 28:749

Hafs ibn Ghiyath narrated to us, from Ja’far, from his father, that Ali ordered his herald, so he proclaimed on the day of Basra: "Do not pursue one who is fleeing, do not finish off a wounded person, and do not kill a captive. Whoever closes his door is safe, and whoever lays down his weapon is safe. And we shall not take anything of their possessions."