Musannaf Ibn Abi Shayba 28:717

Ibn ‘Ulayyah narrated to us, from Ayyub, from Abu Qilabah, from Abu al-Muhallab, from ‘Imran ibn Husayn, that the Prophet (peace and blessings of Allah be upon him) ransomed two men from the Muslims for one man from the polytheists of Banu ‘Uqayl.