The Gospels of Matthew and Luke describe a miracle in which a man who was blind and mute was taken to Jesus and Jesus healed him. As explained in the book of Matthew:
-Matthew 12:22-23, NIV translation.
The phrase "Son of David" was a way to refer to the Messiah who had been promised by the prophets of the Old Testament. The Messiah was to be a descendant of King David who had lived about a thousand years before Jesus. The Gospels of Matthew and Luke say that Jesus was a descendant of King David, in addition to proclaiming that he is the promised Messiah.