Musnad Ahmad 25:378

'Ali ibn 'Asim narrated to us, Dawud narrated to us, 'Ikrimah narrated from Ibn 'Abbas, who said: "There were some people among the captives on the day of Badr who had no ransom. So the Messenger of Allah (ﷺ) made their ransom that they should teach the children of the Ansar writing." He said: "Then a boy came one day crying to his father. He said: 'What is the matter with you?' He said: 'My teacher hit me.' He said: 'The wicked one, he is seeking revenge for Badr. By Allah, you shall never go to him again.'"