Whenever the Messenger of Allah ﷺ said the opening takbir, he would pause silently between the takbir and the recitation. I said, "May my father and mother be ransom for you, what about your silence between the takbir and the recitation? Tell me what you say."He said, "I say, 'Allah, place a great distance between me and my sins, as great as the distance you have placed between the east and the west. Allah, cleanse me of my sins as a white garment is cleansed of filth. Allah, wash me of my sins with water, snow, and hail.'"
حدثنا أبو بكر بن أبي شيبة وعلي بن محمد قالا حدثنا محمد بن فضيل عن عمارة بن القعقاع عن أبي زرعة
كان رسول الله ﷺ إذا كبر سكت بين التكبير والقراءة قال فقلت بأبي أنت وأمي أرأيت سكوتك بين التكبير والقراءة فأخبرني ما تقول قال أقول اللهم باعد بيني وبين خطاياي كما باعدت بين المشرق والمغرب اللهم نقني من خطاياي كالثوب الأبيض من الدنس اللهم اغسلني من خطاياي بالماء والثلج والبرد
Bukhari narrated it in the Book of Adhan, chapter, "What is Said After the Takbir," hadith no. 744, and Muslim narrated it in the Book of Mosques, chapter, "What is Said Between the Takbir of Ihram and the Recitation," hadith no. 598, from the hadith of Umarah, through the same chain.