Sunan Abu Dawood, Chapter: Purification (Kitab Al-Taharah)

The Prophet (peace_be_upon_him) said: If anyone applies collyrium, he should do it an odd number of times. If he does so, he has done well; but if not, there is no harm. If anyone cleanses himself with pebbles, he should use an odd number. If he does so, he has done well; but if not, there is no harm. If anyone eats, he should throw away what he removes with a toothpick and swallow what sticks to his tongue. If he does so, he has done well; if not, there is no harm. If anyone goes to relieve himself, he should conceal himself, and if all he can do is to collect a heap of send, he should sit with his back to it, for the devil makes sport with the posteriors of the children of Adam. If he does so, he has done well; but if not, there is no harm.