Is the current Modern Standard Arabic the same Arabic language that was prevalent during the time of the Messenger, may God's prayers and peace be upon him, or is it one of the other dialects?

The prevalent language during the era of Prophet Muhammad, peace and blessings be upon him, was Classical Arabic (al-Arabiyyah al-Fus'ha), which is the language of the Holy Quran, the Prophet's hadiths, and his discourses. This is supported by Allah Almighty's statement: "And We did not send any messenger except with the language of his people, so that he might make [the message] clear to them." Interpreters have explained this to mean that messengers were sent with the language of their people so that they could clarify and make understandable what they were sent with. The Arabic language has, by Allah's grace, preserved its purity due to the preservation of the Quran, and it has not changed like other languages. Even the enemies of Islam have testified to this.