Musnad Ahmad 26:75

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Shaqiq, from Abdullah, who said: When we used to sit with the Messenger of Allah (peace and blessings of Allah be upon him) in the prayer, we would say: "Peace be upon Allah before His servants, peace be upon Jibril, peace be upon Mika'il, peace be upon so-and-so, peace be upon so-and-so." The Messenger of Allah (peace and blessings of Allah be upon him) heard us and said: "Indeed, Allah is As-Salam (The Peace). So when one of you sits in the prayer, let him say: 'The greetings are for Allah, and the prayers, and the good things. 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.' For if he says it, it reaches every righteous servant in the heaven and the earth. 'I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and His messenger.' Then let him choose from the supplications whatever he wishes."