From Sahih Bukhari (Hadith 500):
Narrated Anas Ibn Malik:Whenever the Prophet (ﷺ) went for answering the call of nature, I and another boy used to go after him with a staff, a stick or a short spear (or stick) and a tumbler of water and when he finished from answering the call of nature we would hand that tumbler of water to him
Reference: Bukhari 500