Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) used to teach us the tashahhud just as he taught us the Qur'an, and he (peace and blessings be upon him) used to say: "All blessed greetings (acts of worship by the tongue), prayers (acts of worship by the body) and pure words are for Allah. 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 none worthy of worship except Allah, and I bear witness that Muhammad (peace and blessings be upon him) is the Messenger of Allah."
Yahya bin Bukayr said: Al-Layth used to act upon this.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10950