Musnad Ahmad 3895
Musnad of Abdullah bin Mas'ood
it was narrated that ‘Abdullah (رضي الله عنه) said: When we sat in the prayer, we would say: Peace be upon Allah, peace be upon us from our Lord, peace be upon Jibreel and Mika'eel, peace be upon So and so, peace be upon So and so. Then the Messenger of Allah (ﷺ) said: "Allah is as-Salam, so when you sit in the pгаyeг, say: ‘All compliments, prayers and pure words are due to Allah. Peace be upon you, O Prophet (ﷺ), and the mercy of Allah and His blessings. Peace be upon us, and on the righteous slaves of Allah' - for if you say that, it will reach every righteous slave in heaven and on earth - ‘I bear witness that there is no god but Allah, and I bear witness that Muhammad is His slave and Messenger. Then let him choose whatever words he wants."