"The Prophet (ﷺ) wanted to defecate, and he told me to bring him three stones. I found two stones and looked for a third, but I could not find any, so I picked up a piece of dung and brought them to the Prophet (ﷺ). He took the two stones and three away the dung and said: "This is Riks."

Abu 'Abdur-Rahman (An-Nasai') said: Riks is the food of the jinn.
Sunan an-Nasa'i Book 1, Hadith 42
← Previous Hadith "Your companion (meaning, the Prophet(ﷺ)) even teaches you how to go to the toilet!" He said: "Yes, he forbade us from facing the Qiblah when defecating or urinating, or cleaning ourselves with out right hands, or to use less than three stones."

Sunan an-Nasa'i Book 1, Hadith 41 Next Hadith → "When you clean yourselves (with stones, after defecating), use an odd number."

Sunan an-Nasa'i Book 1, Hadith 43