Sunan of Abu Dawood Book 1, Hadith 246

حَدَّثَنَا حُسَيْنُ بْنُ عِيسَى الْخُرَاسَانِيُّ، حَدَّثَنَا ابْنُ أَبِي فُدَيْكٍ، عَنِ ابْنِ أَبِي ذِئْبٍ، عَنْ شُعْبَةَ، قَالَ إِنَّ ابْنَ عَبَّاسٍ كَانَ إِذَا اغْتَسَلَ مِنَ الْجَنَابَةِ يُفْرِغُ بِيَدِهِ الْيُمْنَى عَلَى يَدِهِ الْيُسْرَى سَبْعَ مِرَارٍ ثُمَّ يَغْسِلُ فَرْجَهُ فَنَسِيَ مَرَّةً كَمْ أَفْرَغَ فَسَأَلَنِي كَمْ أَفْرَغْتُ فَقُلْتُ لاَ أَدْرِي ‏.‏ فَقَالَ لاَ أُمَّ لَكَ وَمَا يَمْنَعُكَ أَنْ تَدْرِيَ ثُمَّ يَتَوَضَّأُ وُضُوءَهُ لِلصَّلاَةِ ثُمَّ يُفِيضُ عَلَى جِلْدِهِ الْمَاءَ ثُمَّ يَقُولُ هَكَذَا كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَتَطَهَّرُ ‏.‏

Shu'bah reported :when Ibn ‘Abbas took a bath because of sexual defilement, he poured (water) over his left hand with his right hand seven times. Once he forgot how many times he had poured (water). Therefore he asked me: how many times did I pour (water)? I do not know. He said : may you miss your mother! What prevented you from remembering it? He then performed ablution as he did for prayer and poured water over his skin (body). He then said: this is how the Messenger of Allah (May peace be upon him) purified (himself)