From Sahih Bukhari (Hadith 2537):
Narrated Anas:Some men of the Ansar asked for the permission of Allah's Messenger (ﷺ) and said, "Allow us to give up the ransom from our nephew Al-`Abbas. The Prophet (ﷺ) said (to them), "Do not leave (even) a Dirham (of his ransom)
Reference: Bukhari 2537