The Prophet ﷺ went out to answer the call of nature and asked me to bring three stones. I found two stones and searched for the third but could not find it. So took a dried piece of dung and brought it to him. He took the two stones and threw away the dung and said, "This is a filthy thing."  

أَنَّهُ سَمِعَ عَبْدَ اللَّهِ يَقُولُ أَتَى النَّبِيُّ ﷺ الْغَائِطَ فَأَمَرَنِي أَنْ آتِيَهُ بِثَلاَثَةِ أَحْجَارٍ فَوَجَدْتُ حَجَرَيْنِ وَالْتَمَسْتُ الثَّالِثَ فَلَمْ أَجِدْهُ فَأَخَذْتُ رَوْثَةً فَأَتَيْتُهُ بِهَا فَأَخَذَ الْحَجَرَيْنِ وَأَلْقَى الرَّوْثَةَ وَقَالَ هَذَا رِكْسٌ وَقَالَ إِبْرَاهِيمُ بْنُ يُوسُفَ عَنْ أَبِيهِ عَنْ أَبِي إِسْحَاقَ حَدَّثَنِي عَبْدُ الرَّحْمَنِ