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bukhari:500Muḥammad b. Ḥātim b. Bazīʿ > Shādhān > Shuʿbah > ʿAṭāʾ b. Abū Maymūnah > Anas b. Mālik

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.  

البخاري:٥٠٠حَدَّثَنَا مُحَمَّدُ بْنُ حَاتِمِ بْنِ بَزِيعٍ قَالَ حَدَّثَنَا شَاذَانُ عَنْ شُعْبَةَ عَنْ عَطَاءِ بْنِ أَبِي مَيْمُونَةَ قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ قَالَ

كَانَ النَّبِيُّ ﷺ إِذَا خَرَجَ لِحَاجَتِهِ تَبِعْتُهُ أَنَا وَغُلاَمٌ وَمَعَنَا عُكَّازَةٌ أَوْ عَصًا أَوْ عَنَزَةٌ وَمَعَنَا إِدَاوَةٌ فَإِذَا فَرَغَ مِنْ حَاجَتِهِ نَاوَلْنَاهُ الإِدَاوَةَ  


See similar narrations below:

Collected by Bukhārī
bukhari:151Sulaymān b. Ḥarb > Shuʿbah > Abū Muʿādh > ʿAṭāʾ b. Abū Maymūnah > Anas

Whenever Messenger of Allah 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.  

البخاري:١٥١حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ أَبِي مُعَاذٍ هُوَ عَطَاءُ بْنُ أَبِي مَيْمُونَةَ قَالَ

سَمِعْتُ أَنَسًا يَقُولُ كَانَ رَسُولُ اللَّهِ ﷺ إِذَا خَرَجَ لِحَاجَتِهِ تَبِعْتُهُ أَنَا وَغُلاَمٌ مِنَّا مَعَنَا إِدَاوَةٌ مِنْ مَاءٍ