Sahih Muslim Book 35, Hadith Number 6510.
Chapter : The merit of pronouncing Tablil, Tasbib and supplication.
‘Amr b. Maimun reported: He who uttered: “There is no god but Allah, the One, having no partner with Him, His is the Sovereignty and all praise is due to Him and He is Potent over everything” ten times, he is like one who emancipated four slaves from the progeny of Isma’il. Rabi’ b. Khuthaim narrated a hadith like this. Sha’bi reported: I said to Rabi’: From whom did you hear it? He said: From ‘Amr b. Maimun. I came to ‘Amr b. Maimun and said to him: From whom did you hear this hadith? He said: from Ibn Abi Laila. I came to Ibn Abi Laila and said to him: From whom did you hear this hadith? He said: From Abu Ayyub Ansari, who narrated from Allah’s Messenger (may peace be upon him).