Sahih Muslim 262b
Sahih Muslim · Book 2: The Book of Purification · Cleaning oneself after relieving oneself
Salman said that (one among) the polytheists remarked:
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ ، حَدَّثَنَا سُفْيَانُ ، عَنِ الأَعْمَشِ ، وَمَنْصُورٍ ، عَنْ إِبْرَاهِيمَ ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ يَزِيدَ ، عَنْ سَلْمَانَ ، قَالَ قَالَ لَنَا الْمُشْرِكُونَ إِنِّي أَرَى صَاحِبَكُمْ يُعَلِّمُكُمْ حَتَّى يُعَلِّمَكُمُ الْخِرَاءَةَ . فَقَالَ أَجَلْ إِنَّهُ نَهَانَا أَنْ يَسْتَنْجِيَ أَحَدُنَا بِيَمِينِهِ أَوْ يَسْتَقْبِلَ الْقِبْلَةَ وَنَهَى عَنِ الرَّوْثِ وَالْعِظَامِ وَقَالَ " لاَ يَسْتَنْجِي أَحَدُكُمْ بِدُونِ ثَلاَثَةِ أَحْجَارٍ " .
I see that your friend even teaches you about the excrement. He replied; Yes, he has in fact forbidden us that anyone amongst us should cleanse himself with his right hand, or face the Qibla. He has forbidden the use of dung or bone for it, and he has also instructed us not to use less than three pebbles (for this purpose).