Musannaf Ibn Abi Shayba 38:60

Hafs ibn Ghiyath narrated to us, from Ja’far, from his father, who said: Ali ordered his herald, and 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 casts aside his weapon is safe." And he did not take anything from their possessions.