Sahih Bukhari Volume 001, Book 012, Hadith Number 711.
Narated By Abu Huraira : Allah's Apostle used to keep silent between the Takbir and the recitation of Qur'an and that interval of silence used to be a short one. I said to the Prophet "May my parents be sacrificed for you! What do you say in the pause between Takbir and recitation?" The Prophet said, "I say, 'Allahumma, ba'id baini wa baina khatayaya kama ba'adta baina-l-mashriqi wa-l-maghrib. Allahumma, naqqim min khatayaya kama yunaqqa-ththawbu-l-abyadu mina-ddanas. Allahumma, ighsil khatayaya bil-ma'i wa-th-thalji wal-barad (O Allah! Set me apart from my sins (faults) as the East and West are set apart from each other and clean me from sins as a white garment is cleaned of dirt (after thorough washing). O Allah! Wash off my sins with water, snow and hail.)"