Sunan an-Nasa'i 60
It was narrated that Abu Hurairah said:
"When the Messenger of Allah (ﷺ) started Salah, he would remain silent for a short while. I said: 'May my father and mother be ransomed for you, O Messenger of Allah! What do you say when you remain silent between the Takbir and the recitation (in the Salah)?' He said: 'I say: Allahumma ba'id baini was baina khatayaya kama ba'adta baina al-mashriq wal-maghrib; Allahumma naqqini min khatayaya kama yunaqqath-thawb al-abyad min ad-danas; Allahummaghsilni min khatayaya bith-thalji wal-ma'i wal-barad (O Allah, out a great distance between me and my sins, as great as the distance You have made between the East and the West; O Allah, cleanse me of of sin as a white garment is cleansed from filth; Wash away my sins with snow, water, and hail)'."
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ عُمَارَةَ بْنِ الْقَعْقَاعِ، عَنْ أَبِي زُرْعَةَ بْنِ عَمْرِو بْنِ جَرِيرٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا اسْتَفْتَحَ الصَّلاَةَ سَكَتَ هُنَيْهَةً فَقُلْتُ بِأَبِي أَنْتَ وَأُمِّي يَا رَسُولَ اللَّهِ مَا تَقُولُ فِي سُكُوتِكَ بَيْنَ التَّكْبِيرِ وَالْقِرَاءَةِ قَالَ ‏
"‏ أَقُولُ اللَّهُمَّ بَاعِدْ بَيْنِي وَبَيْنَ خَطَايَاىَ كَمَا بَاعَدْتَ بَيْنَ الْمَشْرِقِ وَالْمَغْرِبِ اللَّهُمَّ نَقِّنِي مِنْ خَطَايَاىَ كَمَا يُنَقَّى الثَّوْبُ الأَبْيَضُ مِنَ الدَّنَسِ اللَّهُمَّ اغْسِلْنِي مِنْ خَطَايَاىَ بِالثَّلْجِ وَالْمَاءِ وَالْبَرَدِ ‏"‏ ‏.‏