Musannaf Ibn Abi Shayba 28:748

Hushaym narrated to us, from Husayn, from Ubayd Allah ibn Abd Allah ibn Utbah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said on the day of the conquest of Mecca: "Beware, no one who is fleeing shall be killed, and no one who is wounded shall be finished off. And whoever closes his door, he is safe."