It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that some of the captives of the Battle of Badr had nothing with which to pay a ransom, so the Messenger of Allah (peace and blessings be upon him) made their ransom that they teach the children of the Ansar to read and write. The narrator says: Once a boy of the Ansar came to his father, who asked: What has happened to you? He said: My teacher beat me. So his father said (in anger): This wretch is seeking revenge for Badr; by Allah, you will never go to him again. This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.