Musannaf Ibn Abi Shaybah 36142 — Book of History

Sayyiduna Ibn Umar (may Allah be pleased with them both) said: On the day of the Battle of Uhud I was presented before the Messenger of Allah (peace and blessings be upon him) when I was fourteen years old. He (peace and blessings be upon him) considered me too young and sent me back. On the day of the Battle of the Trench I was presented before him (peace and blessings be upon him) when I was fifteen years old, and he granted me permission for jihad.