Musnad Ahmad 25:518

Ya'qub narrated to us, Ibn Akhi Ibn Shihab narrated to us, from his uncle, who said: Ubayd Allah ibn Abd Allah ibn Utbah ibn Mas'ud informed me that Ibn Abbas said: I approached, having neared the age of puberty, riding upon a female donkey, while the Messenger of Allah (peace and blessings of Allah be upon him) was standing, leading the people in prayer at Mina, until I arrived in front of a part of the first row. Then I dismounted from it, and it grazed, and I stood in a row with the people behind the Messenger of Allah (peace and blessings of Allah be upon him).