بُلُوغُ الْمَرَامِ
Bulugh al-Maram 271
The Book of Prayer
وَعَنْ أَبِي هُرَيْرَةَ - رضى الله عنه - قَالَ : { كَانَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -إِذَا كَبَّرَ لِلصَّلَاةِ سَكَتَ هُنَيَّةً , قَبْلِ أَنْ يَقْرَأَ , فَسَأَلْتُهُ , فَقَالَ : "أَقُولُ : اَللَّهُمَّ بَاعِدْ بَيْنِي وَبَيْنَ خَطَايَايَ كَمَا بَاعَدْتَ بَيْنَ اَلْمَشْرِقِ وَالْمَغْرِبِ , اَللَّهُمَّ نقِّنِي مِنْ خَطَايَايَ كَمَا يُنَقَّى اَلثَّوْبُ اَلْأَبْيَضُ مِنْ اَلدَّنَسِ , اَللَّهُمَّ اِغْسِلْنِي مِنْ خَطَايَايَ بِالْمَاءِ وَالثَّلْجِ وَالْبَرَدِ } مُتَّفَقٌ عَلَيْهِ [1]
Narrated Abu Hurairah (RA) Allah's Messenger (ﷺ) used to keep silent - between the opening Takbir of the prayer and the recitation of the Qur'an - for a short while. Then, I asked him (about that) and he replied, "I say, 'O Allah! Keep me apart from my sins (faults) as you have kept apart the east and west. O Allah clean me from my sins as a white garment is cleaned from dirt. O Allah wash me of my sins with water, snow and hail." [Agreed upon].
Sunnah.com reference: Book 2, Hadith 150