It is narrated from Ibn Abbas (may Allah be pleased with them both) that he said: The Messenger of Allah (ﷺ) used to teach us the Tashahhud just as he used to teach us the Qur'an, and he (ﷺ) would say: "All blessed words, physical acts, and wealth are for Allah. O Prophet (ﷺ)! Peace be upon you, 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 deity except Allah, and I bear witness that Muhammad (ﷺ) is the Messenger of Allah."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 254
Hadith Takhrijأخرجہ مسلم، الصلاۃ، باب التشہد فی الصلاۃ: 403۔