The Book of Purification
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، وَأَبُو كُرَيْبٍ - وَاللَّفْظُ لِزُهَيْرٍ - حَدَّثَنَا إِسْمَاعِيلُ، - يَعْنِي ابْنَ عُلَيَّةَ - حَدَّثَنِي رَوْحُ بْنُ الْقَاسِمِ، عَنْ عَطَاءِ بْنِ أَبِي مَيْمُونَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَتَبَرَّزُ لِحَاجَتِهِ فَآتِيهِ بِالْمَاءِ فَيَتَغَسَّلُ بِهِ .Anas b. Malik reported:The Messenger of Allah (ﷺ) went to a far-off place in the desert (hidden from the sight of human beings) for relieving himself. Then I brought water for him and he cleansed himself
From Sahih Muslim, whose reports the scholars accept as authentic.