The Messenger of Allah ﷺ addressed us, explaining our practice and teaching us how to pray. He said, "When you sit, let the first words any of you says be, 'All greetings, good things, and prayers 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. I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and messenger.'"
إن رسول الله ﷺ خطبنا فبين لنا ستنا، وعلمنا صلاتنا فقال: وإذا كان عند القعدة فليكن من أول قول أحدكم: التحيات الطيبات الصلوات الله، السلام عليك أيها النبي ورحمة الله وبركاته، السلام علينا وعلى عباد الله الصالحين، أشهد أن لا إله إلا الله، وأشهد أن محمدا عبده ورسوله.
Muslim narrated it in the chapter on prayer (404), from Hittan bin Abdullah Raqashi, who said, "I prayed with Abu Musa Ashari a prayer," then he mentioned a long hadith, and this is part of it.