It is narrated from Sayyiduna Zayd bin Harithah (may Allah be pleased with him) that on the day of Uhud the Messenger of Allah (peace and blessings be upon him) (did not permit) some people (to take part in the fighting) on account of their young age, and among them was Sayyiduna Zayd bin Arqam (may Allah be pleased with him).
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4943