He witnessed Abdul-Rahman bin Awf asking Bilal about the ablution of the Messenger of Allah ﷺ.Bilal replied, "He would go out to relieve himself, and I would bring him water. He would then perform ablution, wiping over his turban and his leather socks."
حدثنا عبيد الله بن معاذ حدثنا أبي حدثنا شعبة عن أبي بكر يعني ابن حفص بن عمر بن سعد سمع أبا عبد الله
أنه شهد عبد الرحمن بن عوف يسأل بلالا عن وضوء رسول الله ﷺ فقال كان يخرج يقضي حاجته فآتيه بالماء فيتوضأ ويمسح على عمامته وموقيه
[Hasan] It was reported by Hakim: 1/170, from the hadith of Ubaydullah bin Muaz, in this manner. Hakim graded it sahih, and Dhahabi agreed with him. The hadith has very many corroborating narrations.