Musnad Ahmad 26:551

Yahya narrated to us, from al-A’mash, Shaqiq narrated to me, from Abdullah, who said: When we sat with the Messenger of Allah (peace and blessings of Allah be upon him) in the prayer, we used to say: "Peace be upon Allah from His servants, peace be upon so-and-so, and so-and-so." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not say: 'Peace be upon Allah,' for Allah is the Peace (as-Salam). But when one of you sits, let him say: 'The greetings (at-tahiyyat) 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 you say that, it reaches every righteous servant between 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 one of you choose from the supplications what is most pleasing to him, and let him supplicate with it."