Mishkat al-Masabih #436

Shu'ba said that when Ibn ‘Abbas washed because of seminal defilement he emptied water seven times from his right hand over his left hand, then washed his private parts. Once he forgot how often he had emptied it, so he asked Shu'ba, but he replied that he did not know, so he said, “You should be ashamed of yourself. What prevents you from knowing?” Then he would perform his ablution for prayer, then pour water over his body and say, “Thus was God’s messenger accustomed to purify himself.” Abu Dawud transmitted it.