Mark 10:47

And when he heard that it was Jesus the Nazarene, he began to cry out, and say, Jesus, thou Son of David, have mercy on me.

Luke gave the detail of the blind man's inquiry which prompted the reply to it recorded here.

Thou Son of David ... This was a common title of the expected Messiah in use throughout Israel in the times of Christ; and there is no way to deny the implications of it as used by Bartimaeus. Significantly, the Pharisees were blind to the fact of Jesus being truly the Son of David, but the blind not only knew it but shouted it to high heaven. This is a clear case of the blind seeing and the seeing being blind as mentioned in John 9:39f.