I said to Ibn Umar, "I see you wearing these tanned leather sandals and performing ablution in them."He replied, "I saw the Messenger of Allah ﷺ wearing them and performing ablution in them."
أخبرنا محمد بن العلاء قال حدثنا ابن إدريس عن عبيد الله ومالك وابن جريج عن المقبري
قلت لابن عمر رأيتك تلبس هذه النعال السبتية وتتوضأ فيها قال رأيت رسول الله ﷺ يلبسها ويتوضأ فيها
Bukhari transmitted it, Wudu, chapter on washing the feet while wearing sandals etc., no. 166, and Muslim, Hajj, chapter on entering the state of ihram from the place where the mount sets off, no. 1187, from the hadith of Malik through this route, and it is in Muwatta 1/333 at greater length, and Kubra, no. 118.