Narrated Marwan bin Al-Hakam and Al-Miswar bin Makhrama:

When the delegates of the tribe of Hawazin came to the Prophet they requested him to return their property and their captives. He said to them, "This concerns also other people along with me as you see, and the best statement to me is the true one, so you may choose one of two alternatives; either the captives or the property and (I have not distributed the booty for) I have been waiting for you."

When the Prophet had returned from Ta'if, he waited for them for more than ten nights. When they came to know that the Prophet would not return except one of the two, they chose their captives. The Prophet then stood up amongst the Muslims, Glorified and Praised Allah as He deserved, and then said, "Then after: These brothers of yours have come to you with repentance and I see it proper to return their captives, so whoever amongst you likes to do that as a favor, then he can do it, and whoever of you wants to stick to his share till we pay him from the very first Fai (i.e. war booty) which Allah will give us, then he can do so." The people said, "We return (the captives) to them willingly as a favor, O Allah's Apostle!" The Prophet said, "I do not know who of you has given his consent and who has not; so go back and your leaders may present your decision to me." The people went away, and their leaders discussed the matter with them, and then came to the Prophet to tell him that all of them had given their consent (to return the captives) willingly.

Bukhari :: Book 3 :: Volume 47 :: Hadith 778