Is the narration that the ransom for some of the prisoners of Badr was teaching ten Muslim children sound?

The report indicating that the Messenger of Allah, peace and blessings be upon him, ransomed some of the prisoners of Badr by having them teach the children of Madinah is found in Imam Ahmad's Musnad and Al-Bayhaqi's Sunan, and it is mentioned in books of Seerah. Its purport is that the ransom for some prisoners who had nothing to offer for their release was to teach the children of the Ansar how to write, and Zayd ibn Thabit was among those who learned from them. Ibn al-Qayyim mentioned that the Prophet, peace and blessings be upon him, ransomed some prisoners for teaching a group of Muslims how to write, but the specification of ten children has not been mentioned in an authentic narration.