Ablutions (Wudu')
4/16. Chapter:
Getting water carried by somebody else for purification (washing one's private parts).
وَقَالَ أَبُو الدَّرْدَاءِ: أَلَيْسَ فِيكُمْ صَاحِبُ النَّعْلَيْنِ وَالطَّهُورِ وَالْوِسَادِ.And Abu Ad-Darda’ said (to the people of Iraq), “Is not the man whose nicknames are Sahib An-Na‘lain, Sahib At-Tahir, and Sahib Al-Wisad (‘Abdullah bin Mas‘ud) amongst you?” [‘Abdullah bin Mas‘ud used to carry the Na‘lain (shoes) and Tahir (water for purification and ablution) and Wisad (carpet) for the Prophet ﷺ, so he was called by those names].
Sahih Bukhari
حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي مُعَاذٍ ـ هُوَ عَطَاءُ بْنُ أَبِي مَيْمُونَةَ ـ قَالَ سَمِعْتُ أَنَسًا، يَقُولُ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا خَرَجَ لِحَاجَتِهِ تَبِعْتُهُ أَنَا وَغُلاَمٌ مِنَّا مَعَنَا إِدَاوَةٌ مِنْ مَاءٍ.
Narrated Anas: Whenever Allah's Messenger (ﷺ) went to answer the call of nature, I along with another boy from us used to go behind him with a tumbler full of water.
Reference : Sahih al-Bukhari 151In-book reference : Book 4, Hadith 17USC-MSA web (English) reference : Vol. 1, Book 4, Hadith 153