The Messenger of Allah ﷺ taught us to say when we sit after two units of prayer, "All greetings, prayers, and good deeds 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."
أخبرنا يعقوب بن إبراهيم الدورقي عن الأشجعي عن سفيان عن أبي إسحق عن الأسود
علمنا رسول الله ﷺ أن نقول إذا جلسنا في الركعتين التحيات لله والصلوات والطيبات السلام عليك أيها النبي ورحمة الله وبركاته السلام علينا وعلى عباد الله الصالحين أشهد أن لا إله إلا الله وأشهد أن محمدا عبده ورسوله
Sahih. Tirmidhi reported it in the book of prayer, chapter on what has been said about the tashahhud, hadith 289, from Yaqub bin Ibrahim, by this route, and it is also in Kubra, hadith 748. Its basic content is agreed upon, reported by Bukhari, hadith 6230, 835, 831, and Muslim, hadith 402.