Luke 18:1, 6-8

And he spake a parable unto them to this end, that men ought always to pray, and not to faint

And the Lord said, Hear what the unjust judge saith. And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them? I tell you that he will avenge them speedily. Nevertheless when the Son of man cometh, shall he find faith on the earth?