It is related in the Shifa’ [Shifa’ Al-Sudur] by Ibn Sabu’, from one of the Companions, who said: I accompanied Him (SAW) on a journey, and when He wanted to fulfill a need, I observed carefully when He went in to a certain place. And He fulfilled His need, and I went in to the place He had come out of, and no trace of defecation or urine could be seen from Him. I saw three stones in that location, so I took them, and I found that they had a pleasant aroma and were perfumed.