Matthew 9

Matthew records that -

"...when Jesus departed thence, two blind men followed him, crying, and saying, Thou Son of David, have mercy on us.
28 And when he was come into the house, the blind men came to him: and Jesus saith unto them, Believe ye that I am able to do this? They said unto him, Yea, Lord.
29 Then touched he their eyes, saying, According to your faith be it unto you."  (Matthew 9:27–29)

I specifically noted that this healing was conditional "according to your faith"