مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2994
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: al-Fadl and I passed by on a donkey when the Messenger of Allah (ﷺ) was leading the people in prayer on some open ground. We dismounted and joined him, and he did not say anything to us about that.
Musnad Ahmad 3017A saheeh hadeeth]