Language:
كتاب الصلاة
8  
Prayers (Salat)
(93)
Chapter: To offer As-Salat (the prayer) using an 'Anaza (a spear-headed stick) (as a Sutra)
(93)
باب الصَّلاَةِ إِلَى الْعَنَزَةِ
Sahih al-Bukhari 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.

حَدَّثَنَا مُحَمَّدُ بْنُ حَاتِمِ بْنِ بَزِيعٍ، قَالَ حَدَّثَنَا شَاذَانُ، عَنْ شُعْبَةَ، عَنْ عَطَاءِ بْنِ أَبِي مَيْمُونَةَ، قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا خَرَجَ لِحَاجَتِهِ تَبِعْتُهُ أَنَا وَغُلاَمٌ وَمَعَنَا عُكَّازَةٌ أَوْ عَصًا أَوْ عَنَزَةٌ وَمَعَنَا إِدَاوَةٌ، فَإِذَا فَرَغَ مِنْ حَاجَتِهِ نَاوَلْنَاهُ الإِدَاوَةَ‏.‏
Reference : Sahih al-Bukhari 500
In-book reference : Book 8, Hadith 147
USC-MSA web (English) reference : Vol. 1, Book 9, Hadith 479
  (deprecated numbering scheme)