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." (Using translation from Bukhārī 156)
أَنَّهُ سَمِعَ عَبْدَ اللهِ بْنَ مَسْعُودٍ يَقُولُ أَتَى النَّبِيُّ ﷺ الْغَائِطَ فَأَمَرَنِي أَنْ آتِيَهُ بِثَلَاثَةِ أَحْجَارٍ فَوَجَدْتُ حَجَرَيْنِ وَالْتَمَسْتُ الثَّالِثَةَ فَلَمْ أَجِدْهُ فَأَخَذْتُ رَوْثَةً فَأَتَيْتُ بِهِنَّ النَّبِيَّ ﷺ فَأَخَذَ الْحَجَرَيْنِ وَأَلْقَى الرَّوْثَةَ وَقَالَ هَذِهِ رِكْسٌ