Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: The Companions used to pray behind the Prophet (peace and blessings be upon him), and one of them said: As-salamu 'ala Allah (Peace be upon Allah). So he (peace and blessings be upon him) said: "Who is the one who said: As-salamu 'ala Allah? Indeed, Allah Himself is al-Salam (the Giver of peace). Rather, say: All verbal, physical and financial acts of worship are for Allah alone. Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous servants of Allah. I bear witness that there is no god but Allah, and I bear witness that Muhammad (peace and blessings be upon him) is His servant and His Messenger."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9848