Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) used to teach us the tashahhud and the sermon just as (he taught us) a surah of the Qur'an: "'At-tahiyyatu lillahi was-salawatu wat-tayyibat, as-salamu 'alayka ayyuhan-nabiyyu wa rahmatullahi wa barakatuh, as-salamu 'alayna wa 'ala 'ibadillahis-salihin, ashhadu an la ilaha illallah, wa ashhadu anna Muhammadan 'abduhu wa rasuluh' (All bodily and financial acts of worship are for Allah. Peace be upon you, O Prophet (peace and blessings be upon him), 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 that Muhammad (peace and blessings be upon him) is His servant and Messenger); and the sermon: 'Innal-hamda lillahi nahmaduhu wa nasta'inuhu wa nastaghfiruhu, wa ashhadu an la ilaha illallahu wa anna Muhammadan 'abduhu wa rasuluh' (All praise is for Allah; we praise Him, and we seek His help and His forgiveness. I bear witness that there is no god but Allah, and that Muhammad (peace and blessings be upon him) is His servant and Messenger); 'And fear Allah, through whom you ask one another, and (respect) the ties of kinship. Indeed, Allah is ever a Watcher over you' [Surah al-Nisa': 1]; 'O you who believe, fear Allah and speak words that are right' [Surah al-Ahzab: 70]; 'He will set right your deeds for you and forgive you your sins, and whoever obeys Allah and His Messenger has certainly attained a great success' [Surah al-Ahzab: 71]."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13831