Sunan at-Tirmidhi (Jami-al-Tirmidhi), Chapter: Taharah (Purification)

narrated that Allah's Messenger (SAW) said, "anyone performs ablution and makes it a perfect ablution and says (I bear witness that there is no God besides Allah who is the One, Who has no partner and I bear witness that Muhammad is His slave and Messenger. 0 Allah! Cause me to be among those who repent and cause me to be among those who purify themselves), then all eight doors of Paradise are opened for him that he may enter whichever door he chooses." [A 17316, 17398, Muslim 234, Abu Dawud 169, 609, Nisai 151, Ibn e Majah 470 ]