Mishkat al-Masabih 352

Abu Huraira reported God’s messenger as saying, “If anyone applies collyrium he should do it an odd number of times. If one does so he has done well, but if not, there is no harm. If anyone cleanses himself with stones he should make use of an odd number. If one 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 he removes with his tongue. If one does so he has done well, but if not, there is no harm. If one goes to relieve himself he should conceal himself, and if all he can do is to collect a heap of sand he should sit with his back to it, for the devil makes sport with the posteriors of the children of Adam. If one does so he has done well, but if not, there is no harm.” Abu Dawud, Ibn Majah and Darimi transmitted it.