Musnad Ahmad 4161

It was narrated from 'Abdullah from the Prophet (ﷺ) that He said in the tashahhud: "All compliments, prayers and pure words are due to Allah, Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us, and upon the righteous slaves of Allah. I bear witness that there is no god but Allah, and I bear witness that Muhammad is His slave and Messenger.”