It is narrated from Sayyiduna Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to say: "When one of you prays, let him say: 'O Allah, put distance between me and my sins as You have put distance between the east and the west. O Allah, I seek refuge in You from having Your face turned away from me on the Day of Resurrection. O Allah, cleanse me of my sins as a white garment is cleansed of dirt. O Allah, keep me alive as a Muslim and cause me to die as a Muslim.'"
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 7018