Sahih Muslim Book 4, Hadith Number 1245.

Chapter : Excellence of Dhikr after prayer and its description.

Abu Huraira reported that Allah’s Messenger (may peace be upon him) used to observe, silence for a short while between the takbir (at the time of opening the prayer) and the recitation of the Qur’an. I said to him: Messenger of Allah, for whom I would give my father and mother in ransom, what do you recite during your period of silence between the takbir and the recitation? He said: I say (these words): ” O Allah, remove my sins from me as Thou hast removed the East from the West. O Allah purify me from sins as a white garment is purified from filth. O Allah !wash away my sins with water, snow and hall.”