Musnad Ahmad 25:1325

'Abd al-Rahman narrated to us, Malik narrated to us, from al-Zuhri, from 'Ubayd Allah ibn 'Abd Allah, from Ibn 'Abbas, who said: I came while the Messenger of Allah (may Allah bless him and grant him peace) was praying at Mina, and I was on a donkey. I left it in front of part of the row, and I entered into the prayer. I had neared the age of puberty, and he did not criticize that.