Musnad Ahmad 421
It was narrated that  Humran bin Aban said:
I saw `Uthman bin `Affan (رضي الله عنه) do wudoo`, He poured water onto his hands three times and washed them, then he rinsed his mouth and nose, then he washed his face three times, then he washed his right arm up to the elbow three times, then the left arm likewise, then he wiped his head, then he washed his right foot three times, then the left foot likewise. He said: I saw the Messenger of Allah (ﷺ)  do wudoo` similar to what I just did, then he said: “Whoever does wudoo` as I just did, then prays two rak’ahs without letting his mind wander, his previous sins will be forgiven”
حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَنْبَأَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ حُمْرَانَ بْنِ أَبَانَ، قَالَ رَأَيْتُ عُثْمَانَ بْنَ عَفَّانَ رَضِيَ اللَّهُ عَنْهُ تَوَضَّأَ فَأَفْرَغَ عَلَى يَدَيْهِ ثَلَاثًا فَغَسَلَهُمَا ثُمَّ مَضْمَضَ وَاسْتَنْثَرَ ثُمَّ غَسَلَ وَجْهَهُ ثَلَاثًا ثُمَّ غَسَلَ يَدَهُ الْيُمْنَى إِلَى الْمِرْفَقِ ثَلَاثًا ثُمَّ الْيُسْرَى مِثْلَ ذَلِكَ ثُمَّ مَسَحَ بِرَأْسِهِ ثُمَّ غَسَلَ قَدَمَهُ الْيُمْنَى ثَلَاثًا ثُمَّ الْيُسْرَى مِثْلَ ذَلِكَ قَالَ رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ تَوَضَّأَ نَحْوًا مِنْ وُضُوئِي هَذَا ثُمَّ قَالَ مَنْ تَوَضَّأَ وُضُوئِي هَذَا ثُمَّ صَلَّى رَكْعَتَيْنِ لَا يُحَدِّثُ فِيهِمَا نَفْسَهُ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ‏.‏