Sahih al-Bukhari 164

Narrated Humran:(the freed slave of `Uthman bin `Affan) I saw `Uthman bin `Affan asking (for a tumbler of water) to perform ablution (and when it was brought) he poured water from it over his hands and washed them thrice and then put his right hand in the water container and rinsed his mouth and washed his nose by putting water in it and then blowing it out. Then he washed his face thrice and (then) forearms up to the elbows thrice, then passed his wet hands over his head and then washed each foot thrice. After that `Uthman said, "I saw the Prophet (ﷺ) performing ablution like this of mine, and he said, 'If anyone performs ablution like that of mine and offers a two-rak`at prayer during which he does not think of anything else (not related to the present prayer) then his past sins will be forgiven. '