Musnad Ahmad 25:1326

I read this hadith to Abd al-Rahman. He said: I arrived riding a female donkey, and I had at that time approached the age of puberty, while the Messenger of Allah (peace and blessings of Allah be upon him) was leading the people in prayer. I passed in front of a part of the row, then I dismounted and let the donkey go, and I entered into the row, and no one disapproved of that for me.