What are the proofs relied upon by those who say that the Syriac language is the mother tongue of Adam and Abraham, and not Arabic? And is it wrong to describe the Prophet (peace be upon him) and the people of the Arabian Peninsula as "Arabized Arabs" even though the Qur'an was revealed in a clear Arabic tongue?

The language spoken by Adam (peace be upon him) is a matter of disagreement. The majority of Usulis (scholars of Islamic jurisprudence) believe that he was taught the fundamentals of all languages. The popular view is that it was Syriac. This was mentioned in the hadith of Abu Dharr (may Allah be pleased with him) that four prophets were Syriac: Adam, Seth, Enoch, and Noah. It was also said that Syriac and Arabic are one language that changed with the change of the inhabitants' dwellings. There are other opinions that it was Greek, Hebrew, or Arabic. Some scholars believe that Adam mostly spoke Syriac, but he knew all languages.