Please advice if the following is authentic: "Attahiyat recited during salah is actually a part of the conversation between Allah SWT and Prohpet Mohammed (SAW) when he met HIM while on Miraj."

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

What you mentioned is not true at all. This is a common saying of many preachers and people who are not knowledgeable of the science of Hadeeth. They say that the wording of Tashahhud originated from a conversation between Allaah Almighty and His Prophet on the night of Mi’raaj (Ascension to the heavens), namely that the Prophet said: “All compliments, prayers, and pure words and deeds, are due to Allaah.” Allaah said: “Peace be upon you O Prophet, and the Mercy of Allaah and His Blessings be upon you.” Then, the Prophet said: “Peace be upon us and on the righteous slaves of Allaah.” Then, the angels said: “I bear witness that there is no god but Allaah and I bear witness that Muhammad is the Messenger of Allaah.”

All this is fabricated and it has no foundation in the books of Sunnah. The Fataawa of the Permanent Committee said: “As regards the Prophet receiving the Tashahhud while prostrating himself (before Allaah) near the Lote Tree in the Highest Heaven on the night of Mi’raaj, we do not know of any foundation for that or for the prostration at that place on the night of Al-Mi’raaj.”

Allaah Knows best.