Authentic Supplication Number 73.

When the Messenger of Allah would start his Salat he would be silent for a moment before beginning to recite. So Abu Hurayrata said: O’ Messenger of Allah! With my father, and my mother [I would sacrifice them for you], you know your silence between the takheer and the recitation, what are you saying [during it]? He said: I say: ‘Allahumma ba`id baynee wa bayna khatayaya kama ba`adta bayna ‘almashriqi wal-maghribi, ‘allahumma naqqinee min khatayaya kama yunaqqa ‘ath-thawbul ‘abyadhu min ‘addanasi, ‘allahumma ‘ighsilnee min khatayaya bith-thalji wal-ma’i wal-baradi (88).

(88) O’ my ‘ilah make distance between myself and my wrong-doings as You have made distance between the East and the West, O’ my ‘ilah purify me of my wrong-doings as a white garment is purified of dirt, O’ my ‘ilah wash me of my wrong-doings with snow, water, and hail.

Agreed upon by Bukhari and Muslim, and Al-Albani included this hadeeth in The Authentic of Good Sayings as #61.