It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that I and Fadl bin Abbas (may Allah be pleased with them both) came riding on a donkey while the Messenger of Allah (peace and blessings be upon him) was leading the prayer. We passed in front of part of the row with the donkey, dismounted from the donkey, left it to graze, and joined the prayer with the Messenger of Allah (peace and blessings be upon him). He did not say anything to us.
Hadith Referenceالسنن المأثورة / باب ما جاء في الصلاة على الراحلة / 125
Hadith Takhrijصحیح مسلم، الصلاة، باب سترة المصلی، رقم: 504