He used to report that the Prophet ﷺ entered into ihram when his mount stood upright with him on it.
أخبرنا عمران بن يزيد قال أنبأنا شعيب قال أنبأنا ابن جريج قال أخبرني صالح بن كيسان ح و أخبرني محمد بن إسمعيل بن إبراهيم قال حدثنا إسحق يعني ابن يوسف عن ابن جريج عن صالح بن كيسان عن نافع
أنه كان يخبر أن النبي ﷺ أهل حين استوت به راحلته
Bukhari recorded it in the Book of Hajj, chapter of one who declares ihram when his mount stands upright, hadith no. 1552, and Muslim in the Book of Hajj, chapter clarifying that it is preferable to enter ihram when one's mount sets off heading toward Makkah..., hadith no. 28/1187, from the hadith of Ibn Jurayj through this same chain, and it is also found in al-Kubra, hadith no. 3740.Shuayb is Ibn Ishaq, and Ishaq is al-Azraq.