Sahih al-Bukhari 6184

Musaddad narrated to us: Yahya narrated to us, from Sufyan, who said: Sad ibn Ibrahim told me, from Abdullah ibn Shaddad, from Ali, may Allah be pleased with him, who said: I never heard the Messenger of Allah, peace and blessings be upon him, offer himself as ransom for anyone except Sad. I heard him say, ‘Shoot; may my father and mother be your ransom.’ I think this was on the day of Uhud.