Sahih Muslim 237c
Abu Huraira reported:
The Messenger of Allah (way peace he upon him) said: When anyone performs ablution he must clean his nose and when anyone wipes himself with pebbles (after answering the call of nature) he must do that odd number of times.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي إِدْرِيسَ الْخَوْلاَنِيِّ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ مَنْ تَوَضَّأَ فَلْيَسْتَنْثِرْ وَمَنِ اسْتَجْمَرَ فَلْيُوتِرْ ‏"‏ ‏.‏