سنن ابن ماجه

It was narrated from Abu Hurairah that: The Prophet (ﷺ) said: "Whoever uses stones to clean himself, let him use an odd number of stones. Whoever does that has done well, and whoever does not, there is no harm in it. Whoever uses a tooth stick should spit out (whatever he removes) and whoever removes (the particle of food) by dislodging it with his tongue should swallow it. Whoever does that has done well, and whoever does not, tere is no harm in it. Whoever goes to the toilet should conceal himself, and if he cannot find anything except a pile of sand (behind which to conceal himself), then he should use that, for the Shaitan plays with the backside of the son of Adam. Whoever does that has done well, and whoever does not, there is no harm in it."