Musnad Ahmad 26:639

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Sulayman, and Mansur, and Hammad, and al-Mughirah, and Abu Hashim, from Abu Wa'il, from Abdullah, from the Prophet, may Allah bless him and grant him peace, that he said: "In the Tashahhud: 'The greetings (at-tahiyyat) are for Allah, and the prayers (as-salawat), and the good things (at-tayyibat). 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 is His servant and His messenger.'"