Musnad Ahmad 26:871

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Hammad, who said: I heard Abu Wa'il saying: Abdullah said: We used to say in the greeting, "Peace be upon Allah." The Messenger of Allah (ﷺ) said: "Do not say, 'Peace be upon Allah,' for Allah is the Peace (As-Salam). Rather, say: 'All compliments, prayers, and pure words are for Allah. 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. I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and His messenger.'"