Prove it. No one to date has been able to. That includes those who keep promoting that lie.
As you probably know, a fragment from the work of Papias (c. 110 AD) states that Matthew was originally written in Aramaic or Hebrew, but we have no extant copies. Since this gospel was written by a Jew, Matthew the tax-collector, for a Jewish Christian audience, he would have spoken the same language as Jesus, Aramaic.
Because of its rich theological content, Matthew was used as the primary catechetical text in the early Church and was the gospel most quoted by the fathers. It presents a holistic and systematic perspective on Jesus, giving an account of his miracles and teachings while placing them in their historical and religious context.