Sahih Bukhari Volume 002, Book 022, Hadith Number 294.
Narated By 'Abdullah bin Masud : We used to say the greeting, name and greet each other in the prayer. Allah's Apostle heard it and said: "Say, 'At-tahiyyatu lil-lahi was-salawatu wat-taiyibatu. Assalamu 'Alaika aiyuha-n-Nabiyu wa-rahmatu-l-lahi wa-barakatuhu. Assalamu alaina wa-'ala 'ibadi-l-lahi as-salihin... Ashhadu an la ilaha illa-l-lah wa ashhadu anna Muhammadan 'abdu hu wa Rasuluh. (All the compliments are for Allah and all the prayers and all the good things (are for Allah). Peace be on you, O Prophet, and Allah's mercy and blessings (are on you). And peace be on us and on the good (pious) worshipers of Allah. I testify that none has the right to be worshipped but Allah and that Muhammad is His slave and Apostle.) So, when you have said this, then you have surely sent the greetings to every good (pious) worship per of Allah, whether he be in the Heaven or on the Earth."