(1) باب التَّخَلِّي عِنْدَ قَضَاءِ الْحَاجَةِ
Narrated Jabir ibn Abdullah:
When the Prophet (ﷺ) felt the need of relieving himself, he went far off where no one could see him.
Reference: Sunan Abi Dawud 2
In-book reference: Book 1, Hadith 2
English translation: Book 1, Hadith 2