At the beginning of the prayer
اَللّٰهُمَّ بَاعِدْ بَيْنِيْ وَبَيْنَ خَطَايَايَ كَمَا بَاعَدْتَّ بَيْنَ الْمَشْرِقِ وَالْمَغْرِبِ، اَللّٰهُمَّ نَقِّنِيْ مِنْ خَطَايَايَ كَمَا يُنَقَّى الثَّوْبُ الْأَ بْيَضُ مِنَ الدَّنَسِ، اَللّٰهُمَّ اغْسِلْنِيْ مِنْ خَطَايَايَ بِالثَّلْجِ والْمَاۗءِ وَالْبَرَدِ
O Allah, distance me from my sins as You have distanced the East from the West. O Allah, purify me of my sins as the white robe is cleansed of filth. O Allah, cleanse me of my sins with snow, water and hail.
References
[Sahih Muslim - 598]