Whenever Messenger of Allah ﷺ went to answer the call of nature, I along with another boy used to accompany him with a tumbler full of water. (Hisham commented, "So that he might wash his private parts with it.)"  

سَمِعْتُ أَنَسَ بْنَ مَالِكٍ يَقُولُ كَانَ النَّبِيُّ ﷺ إِذَا خَرَجَ لِحَاجَتِهِ أَجِيءُ أَنَا وَغُلاَمٌ مَعَنَا إِدَاوَةٌ مِنْ مَاءٍ يَعْنِي يَسْتَنْجِي بِهِ