the overwhelming testimony of early church historians confirm the book of Matthew to be a legitimate christian document. Matthew was one of Jesus chosen apostles, so he was an intimate acquaintance of Jesus and he was an eyewitness of many of the things he wrote about.
From as far back as Papias of Hierapolis (early second century C.E.) onward, there is a line of early witnesses to the fact that Matthew wrote this Gospel and that it is an authentic part of the Word of God. Its in harmony with the rest of the gospels and it was used by the early church to establish the truth of Jesus life and teachings.
McClintock and Strongs Cyclopedia states: Passages from Matthew are quoted by Justin Martyr, by the author of the letter to Diognetus (see in Ottos Justin Martyr, vol. ii), by Hegesippus, Irenæus, Tatian, Athenagoras, Theophilus, Clement, Tertullian, and Origen. It is not merely from the matter, but the manner of the quotations, from the calm appeal as to a settled authority, from the absence of all hints of doubt, that we regard it as proved that the book we possess had not been the subject of any sudden change.