Musannaf Ibn Abi Shayba 38:22

Yahya ibn Adam narrated to us, he said: Sharik narrated to us, from al-Suddi, from Abd Khayr, from Ali, that he said on the Day of the Camel: "Do not pursue one who is fleeing, and do not finish off one who is wounded. And whoever casts aside his weapon, he is safe."