Sahih Muslim Book 002, Hadith Number 0451.
Chapter : The merit of Wudu and that of prayer after it.
'Uqba b. 'Amir reported: We were entrusted with the task of tending the camels. On my turn when I came back in the evening after grazing them in the pastures, I found Allah's Messenger (may peace be upon him) stand and address the people. I heard these words of his: If any Muslim performs ablution well, then stands and prays two rak'ahs setting about them with his heart as well as his face, Paradise would be guaranteed to him. I said: What a fine thing is this ! And a narrator who was before me said: The first was better than even this. When I cast a glance, I saw that it was 'Umair who said: I see that you have just come and observed: If anyone amongst you performs the ablution, and then completes the ablution well and then says: I testify that there is no god but Allah and that Muhammad is the servant of Allah and His Messenger, the eight gates of Paradise would be opened for him and he may enter by whichever of them he wishes.