Sayyiduna Zayd bin Jariyah (may Allah be pleased with him) said that on the day of Uhud the Prophet (peace and blessings be upon him) did not permit some people to take part because they were too young; among them were Zayd bin Jariyah - meaning himself - al-Bara' bin Azib, Sa'd bin Khaythamah, Abu Sa'id al-Khudri, Abdullah bin Umar and Jabir bin Abdullah (may Allah be pleased with them).
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5131