The Messenger of Allah ﷺ would go to relieve himself, and I, along with a boy of about my age, would carry a small water vessel and a spear-like staff (anazah) for him, and he would clean himself with the water.
حدثنا محمد بن جعفر حدثنا شعبة عن عطاء بن أبي ميمونة أنه
كان رسول الله ﷺ يدخل الخلاء فأحمل أنا وغلام نحوي إداوة من ماء وعنزة فيستنجي بالماء
Its isnad is sahih, and it is in the Sahihayn. Bukhari narrated it, 1/252, no. 152, in the chapter on wudu, carrying the spear along with the water, and Muslim, 1/227, no. 271, in the chapter on purification, cleansing with water after relieving oneself.