Acts 20:28-31

Be on guard for yourselves and for all the flock that the Holy Spirit has appointed you to as overseers, to shepherd the church of God, which He purchased with His own blood. I know that after my departure savage wolves will come in among you, not sparing the flock. And men will rise up from your own number with deviant doctrines to lure the disciples into following them. Therefore be on the alert, remembering that night and day for three years I did not stop warning each one of you with tears.