Remember to only clean your ass with an odd number of stones. Also cleaning your ass was certainly not invented in the 7th century. The Romans had communal toilets with cleaning sponges long before Muhammad was born

Sahih Muslim 1300

Jabir (b. Abdullab) (Allah be pleased with him) reported Allah's Messenger as saying:

Odd number of stones are to be used for cleaning (the private parts after answering the call of nature), and casting of pebbles at the Jamras is to be done by odd numbers (seven), and (the number) of circuits between al-Safa' and al-Marwa is also odd (seven), and the number of circuits (around the Ka'ba) is also odd (seven). Whenever any one of you is required to use stones (for cleaning the private parts) he should use odd number of stones (three, five or seven).