Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Ibn Umar (may Allah be pleased with them): I was presented to the Noble Prophet (peace and blessings be upon him) on the day of Uhud, and I was fourteen years old. So the Prophet (peace and blessings be upon him) considered me too young. (Then) I was presented to the Prophet (peace and blessings be upon him) on the day of Khandaq, and I was fifteen years old. So the Prophet (peace and blessings be upon him) granted me permission (to participate in jihad). Hazrat Nafi’ says: I narrated this hadith to Hazrat Umar bin Abdul Aziz, so he said: This (age) is the dividing line between a minor and an adult. Then he wrote to his governor, instructing that those who are fifteen years old should be included among the fighters, and those who are fourteen years old should be included among the children.