Volume 3 · Book 46 · Hadith 714
Narrated Anas: Some men of the Ansar asked for the permission of Allah's Apostle and said, "Allow us to give up the ransom from our nephew Al-'Abbas. The Prophet said (to them), "Do not leave (even) a Dirham (of his ransom)."
— Sahih Bukhari, Volume 3, Book 46: Manumission of Slaves, Hadith #714