Full Sharh — Mishkat al-Masabih 344
وَعَن سلمَان قَالَ قَالَ لَهُ بعض الْمُشْركين وَهُوَ يستهزئ بِهِ إِنِّي لأرى صَاحبكُم يعلمكم كل شَيْء حَتَّى الخراءة قَالَ أَجَلْ أَمَرَنَا أَنْ لَا نَسْتَقْبِلَ الْقِبْلَةَ وَلَا نَسْتَنْجِيَ بِأَيْمَانِنَا وَلَا نَكْتَفِيَ بِدُونِ ثَلَاثَةِ أَحْجَارٍ لَيْسَ فِيهَا رَجِيعٌ وَلَا عَظْمٌ. رَوَاهُ مُسْلِمٌ وَأحمد وَاللَّفْظ لَهُ
English Translation
Salman said that a polytheist jestingly remarked, “I see that your friend teaches you even about your excrement,” to which he replied, “Yes, he has commanded us not to face the qibla, or cleanse ourselves with our right hands, or be satisfied with less than three stones among which there is no dung or bone.” Muslim and Ahmad transmitted it, the wording being Ahmad’s.
Source
Mishkat al-Masabih(مشكاة المصابيح)
Purification
Hadith Number
344