Majma al-Zawaid — Hadith 6647

Abu al-Mu'arik narrates: A man from Ghafiq was owed one hundred dinars by a man from the tribe of Mahrah; this was in the time of Sayyiduna Uthman (may Allah be pleased with him). They obtained good spoils, and the Mahri said: "I will pay you seventy dinars right away on condition that you erase the record of the hundred from me (that is, let go of the rest)," although the hundred was due to be paid later. The Ghafiqi agreed to this. Sayyiduna al-Miqdad (may Allah be pleased with him) passed by the two of them, and the man took hold of the reins of his mount in order to make him a witness. When he narrated the whole incident to him, he said: "Both of you have declared war against Allah and His Messenger (that is, you have attempted a transaction of usury (riba))."
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir; I do not know Abu al-Mu'arik, and the remaining narrators of this report are thiqat (trustworthy).