From Sahih Bukhari (Hadith 7176):
Narrated `Urwa bin Az-Zubair:Marwan bin Al-Hakam and Al-Miswar bin Makhrama told him that when the Muslims were permitted to set free the captives of Hawazin, Allah's Messenger (ﷺ) said, "I do not know who amongst you has agreed (to it) and who has not. Go back so that your 'Urafa' may submit your decision to us." So the people returned and their 'Urafa' talked to them and then came back to Allah's Messenger (ﷺ) and told him that the people had given their consent happily and permitted (their captives to be freed)
Reference: Bukhari 7176