To clean the private parts with odd number of stones

Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "If anyone of you performs ablution he should put water in his nose and then blow it out and whoever cleans his private parts with stones should do so with odd numbers. And whoever wakes up from his sleep should wash his hands before putting them in the water for ablution, because nobody knows where his hands were during sleep."