The Messenger of Allah ﷺ used to teach us the tashahhud just as he would teach us a surah from the Quran. He would say, "Blessed greetings, pure 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 the Messenger of Allah."
كان رسول الله ﷺ يعلمنا التشهد كما يعلمنا السورة من القرآن. فكان يقول: التحيات المباركات، الصلوات الطيبات الله، السلام عليك أيها النبي ورحمة الله وبركاته، السلام علينا وعلى عباد الله الصالحين، أشهد أن لا إله إلا الله، وأشهد أن محمدا رسول الله.
Muslim narrated it in the Book of Prayer (403) from Qutayba bin Saeed, who said, Layth (that is, Ibn Saad) narrated to us from Abu Zubayr, from Saeed bin Jubayr and from Tawus, from Ibn Abbas, and he related it.Abu Awana said in his Sahih (2024), I heard Muhammad bin Abdullah bin Abdul-Hakam say, I heard Shafii say, "This is the best hadith narrated from the Prophet ﷺ concerning the tashahhud."