Praise be to Allah.
These are some of the versions of the Tashahhud which are narrated from the Prophet (peace and blessings of Allaah be upon him).
1 – Ibn Mas’ood (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) taught me the Tashahhud, holding my hand between his hands, just as he would teach me a Soorah from the Qur’aan:
‘At-tahiyyaatu Lillaahi wa’s-salawaatu wa’t-tayyibaat, as-salaamu ‘alayka ayyuha’n-Nabiyyu wa rahmat-Allaahi wa barakaatuhu. As-salaamu ‘alayna wa ‘alaa ‘ibaad-Illaah is-saaliheen. Ash-hadu an laa ilaaha ill-Allaah wa ash-hadu anna Muhammadan ‘abduhu wa rasooluhu (All compliments, prayers and pure words are due to Allaah. Peace be upon you, O Prophet, and the mercy of Allaah and His blessings. Peace be upon us, and on the righteous slaves of Allaah. I bear witness that none has the right to be worshipped except Allaah, and I bear witness that Muhammad is His slave and Messenger).’
This was whilst he was among us, but after he was taken, we would say ‘as-salaam ‘ala’n-Nabi (peace be upon the Prophet (peace and blessings of Allaah be upon him)).’”
(Narrated by al-Bukhaari, al-Isti’dhaan, 6265)
This is the soundest version of the wording of the Tashahhud according to the scholars. This should be said in the first Tashahhud, and in the second Tashahhud there should be added to it al-Salaah ‘ala’n-Nabi (sending blessings upon the Prophet (peace and blessings of Allaah be upon him)). Ibn al-Qayyim said: “It is prescribed for his ummah to send blessings upon him in the last Tashahhud.” (al-Salaah wa Hukm Taarikihaa, 1/284)
2 – The Messenger of Allaah (peace and blessings of Allaah be upon him) said:
“Say: ‘Allaahumma salli ‘ala Muhammadin wa ‘ala aali Muhammadin kamaa salayta ‘ala aali Ibraaheem, wa baarik ‘ala Muhammadin wa ‘ala aali Muhammadin kamaa baarakta ‘ala aali Ibraaheem fi’l-‘aalameen innaka Hameedun Majeed (O Allaah, send prayer upon Muhammad and upon the family of Muhammad, as You sent prayers upon the family of Ibraaheem. And send blessings upon Muhammad and upon the family of Muhammad, as You sent blessings upon the family of Ibraaheem among the nations; You are indeed Worthy of Praise, Full of Glory)’ – and the salaam is as you know.”
(Narrated by Muslim, al-Salaah, 405)
The Sunnah is to make du’aa’ (supplication) after the Tashahhud and before the tasleem (salaams). See Question # 5236