Whenever the Messenger of Allah ﷺ went out to relieve himself, I would bring him water with which he would wash.
حدثنا إسماعيل بن إبراهيم حدثنا روح بن القاسم عن عطاء بن أبي ميمونة
كان رسول الله ﷺ إذا تبرز لحاجته أتيته بماء فيغسل به
Its isnad is sahih. Bukhari related the hadith in 1/64 in the book of wudu, in the chapter on what has been said about washing off urine, and it is found in all the Sahih collections.