Men ought always to pray and not to faint

Luke 18:1-7 (KJV)

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

2 Saying, There was in a city a judge, which feared not God, neither regarded man:

3 And there was a widow in that city; and she came unto him, saying, Avenge me of mine adversary.

4 And he would not for a while: but afterward he said within himself, Though I fear not God, nor regard man;

5 Yet because this widow troubleth me, I will avenge her, lest by her continual coming she weary me.

6 And the Lord said, Hear what the unjust judge saith.

7 And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them?