Muwatta Malik 353

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ عَمْرِو بْنِ يَحْيَى الْمَازِنِيِّ، عَنْ أَبِي الْحُبَابِ، سَعِيدِ بْنِ يَسَارٍ عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُصَلِّي وَهُوَ عَلَى حِمَارٍ وَهُوَ مُتَوَجِّهٌ إِلَى خَيْبَرَ ‏.‏

Yahya related to me from Malik from Amr ibn Yahya al-Mazini from Abu'l-Hubab Said ibn Yasar that Abdullah ibn Umar said, "I saw the Messenger of Allah, may Allah bless him and grant him peace, praying on a donkey while heading towards Khaybar

Reference

Muwatta Malik 353

In-book

Book 9, Hadith 28