Mishkat al-Masabih
Mishkat al-Masabih 344
How to act when relieving oneself - Section 2
Arabic hadith text
وَعَنْ جَابِرٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا أَرَادَ الْبَرَازَ انْطَلَقَ حَتَّى لَا يرَاهُ أحد. رَوَاهُ أَبُو دَاوُد
Translation
Jabir said that when the Prophet wished to relieve himself he went off where no one could see him. Abu Dawud transmitted it.