Sayyiduna Ibn Abbas (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) used to teach us the tashahhud just as he taught us the Qur'an, and he would say: "'At-tahiyyatul-mubarakatus-salawatut-tayyibatu lillah, salamun alayka ayyuhan-nabiyyu wa rahmatullahi wa barakatuh, salamun alayna wa ala ibadillahis-salihin, ashhadu an la ilaha illallah, wa ashhadu anna Muhammadan rasulullah' (All blessed verbal, physical and financial acts of worship are for Allah. Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon all the righteous servants of Allah. I bear witness that there is no deity worthy of worship except Allah, and I bear witness that Muhammad (peace and blessings be upon him) is the Messenger of Allah)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3957