When we sat with the Messenger of Allah ﷺ during the prayer, we used to say, "Peace be upon Allah before His servants, peace be upon Jibril, peace be upon Mikail, peace be upon so-and-so, peace be upon so-and-so."The Messenger of Allah ﷺ heard us and said, "Allah Himself is Peace. When one of you sits during the prayer, let him say, 'All greetings, prayers, and good things belong to Allah. Peace be upon you, Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous servants of Allah.' When he says this, it reaches every righteous servant in the heavens and the earth. 'I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and messenger.' Then let him choose whatever supplication he wishes after that."
حدثنا أبو معاوية حدثنا الأعمش عن شقيق
كنا إذا جلسنا مع رسول الله ﷺ في الصلاة قلنا السلام على الله قبل عباده السلام على جبريل السلام على ميكائيل السلام على فلان السلام على فلان فسمعنا رسول الله ﷺ فقال إن الله هو السلام فإذا جلس أحدكم في الصلاة فليقل التحيات لله والصلوات والطيبات السلام عليك أيها النبي ورحمة الله وبركاته السلام علينا وعلى عباد الله الصالحين فإذا قالها أصابت كل عبد صالح في السماء والأرض أشهد أن لا إله إلا الله وأشهد أن محمدا عبده ورسوله ثم يتخير بعد من الدعاء ما شاء
Its isnad is sahih, and it was narrated by the entire group (of hadith collectors), as noted in Dhakhair 4705. Part of it was mentioned earlier in abbreviated form with a daif isnad, 3562.