Musnad Abu Ya'la al-Mawsili 110:158

Abu Bakr narrated to us, Hafs narrated to us, from al-Hajjaj, from al-Hakam, from Miqsam, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) wrote a document between the Emigrants (Muhajirun) and the Helpers (Ansar) that they should not neglect their blood-money obligations (ma'aqil), and that they should ransom their captives (ani) with kindness and reconciliation among the people.