It was narrated that Ibn`Umar said:
"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).' " (AR)
English reference (AR): Vol. 3, Book 20, Hadith 2543 (AR)
Arabic reference (AR): Book 20, Hadith 2640 (AR)