Yahya bin Abi Kathir يحيى بن أبي كثير الطائي · The Chapters on Legal Punishments

“I was presented to the Messenger of Allah (ﷺ) on the day of Uhud, when I was fourteen years old, but he did not permit me (to fight). I was presented to him on the Day of Khandaq when I was fifteen years old, and he permitted me (to fight).' ”