مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3896
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdullah (رضي الله عنه) said: The Prophet (ﷺ) used to teach us the tashahhud in the prayer: "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 on 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.”
Musnad Ahmad 3921A saheeh hadeeth, al-Bukhari (1202)]