Sahih Bukhari Volume 009, Book 093, Hadith Number 478.

Narrated By 'Abdullah : We used to pray behind the Prophet and used to say: "As-Salamu 'Al-Allah. The Prophet said, "Allah himself is As-Salam (Name of Allah), so you should say: 'At-Tahiyatu lil-laihi was- sala-watu wat-taiyibatu, as-sallamu 'Alayka aiyuha-n-nabiyyu wa rahrmatu-l-lahi wa barak-atuhu, As-salamu 'alaina wa 'ala 'ibaldi-l-lahi as-salihin. Ashhadu an la ilaha il-lallah, wa ash-hadu anna Muhammadan 'abduhu wa rasuluhu.'"