Musnad Ahmad 26:370

Abu Sa’id narrated to us, Za’idah narrated to us, al-A’mash narrated to us, from Shaqiq, from ‘Abdullah, who said: When we used to sit in the prayer, we would say: "Peace be upon Allah, peace be upon us from our Lord, peace be upon Jibril and Mika’il, peace be upon so-and-so, peace be upon so-and-so." The Messenger of Allah (ﷺ) said: "Indeed, Allah is As-Salam (the Peace). So when you sit in the prayer, 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 that, 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 whatever speech he wishes." Sulayman said: Ibrahim also narrated it to me, from al-Aswad, from ‘Abdullah, similar to it.