Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: We did not know what to say in every two rak'ahs of the prayer, except that we would magnify, glorify and praise our Lord. And Muhammad (peace and blessings be upon him) had been given the openings and conclusions of goodness. He (peace and blessings be upon him) said: "When you sit for the tashahhud, say: All verbal, physical and monetary acts of worship are for Allah alone. O Prophet, peace be upon you, 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 deity except Allah, and I bear witness that Muhammad is the servant of Allah and His Messenger."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9881