Explanation

‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported that he was presented to the Messenger of Allah (may Allah's peace and blessings be upon him) in order to join the battle (as a way of presenting the soldiers to the leader). This took place during the Battle of Uhud in the third year after Hijrah. As he was fourteen years old, the Prophet (may Allah's peace and blessings be upon him) refused to allow him to participate due to his young age. Later on, he was presented to him in the year of the battle of Al-Khandaq. This was in the fifth year after Hijrah, and he was fifteen years old. The Prophet (may Allah's peace and blessings be upon him) enlisted him in the forces. Perhaps on the Day of Uhud, ‘Abdullāh ibn ‘Umar had recently turned fourteen years old, while on the Day of Al-Khandaq, he was nearly sixteen years old.