Sahih Bukhari, Chapter: Gifts, The superiority of giving and extortion of

When the delegates of the tribe of Hawazin came to the Prophet (SAW) he stood up amongst the people, Glorified and Praised Allah as He deserved, and said, "Then after: Your brethren have come to you with repentance and I see it logical to return to them their captives; so whoever amongst you likes to do that as a favour, then he can do it, and whoever of you like to stick to his share till we give him his right from the very first Fai (war booty) which Allah will bestow on us, then (he can do so)." The people replied, "We do that (to return the captives) willingly as a favour for your sake."