Sahih Muslim Book 2, Hadith Number 452.

Chapter : The merit of Wudu and that of prayer after it.

Uqba b. ‘Amir al-Juhani reported: Verily the Messenger of Allah (may peace be upon him) said and then narrated (the Hadith) like one (mentioned above) except (this) that he said: He who performed ablution and said: I testify that there is no god but Allah, the One, there is no associate with Him and I testify that Muhammad is His servant and His Messenger.