It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that some men of the Ansar asked permission of the Messenger of Allah (peace and blessings be upon him) and said: "O Messenger of Allah, permit us to let our nephew (sister's son) Abbas off his ransom (by waiving it)." He (peace and blessings be upon him) said: "No, by Allah, you shall not let go of even a single dirham of his ransom."
Only Musa bin Uqbah (may Allah have mercy on him) narrated this hadith from Imam al-Zuhri (may Allah have mercy on him).
Hadith Referenceالمعجم الأوسط / باب العين / 4624
Hadith Takhrij«أخرجه البخاري فى «صحيحه» برقم: 2537، 3048، 4018، وابن حبان فى «صحيحه» برقم: 4794، والحاكم فى «المستدرك» برقم: 5449، والبيهقي فى «السنن الكبرى» برقم: 12277، 12971، 18117، وأبو يعلى فى «مسنده» برقم: 3615، والبزار فى «مسنده» برقم: 6355 (م)، 6356، 6357»