Sahih Muslim
The Book of Purification (Kitab Al-Taharah)
Book Number: 002 / Hadith Number: 452
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.