The Acts 20:28-31

Take heed therefore to yourselves, and to all the flock, wherein the Holy Spirit has set you as overseers, to shepherd the assembly of God, which he has purchased with the blood of his own. For I know this, that there will come in amongst you after my departure grievous wolves, not sparing the flock; and from among your own selves shall rise up men speaking perverted things to draw away the disciples after them. Wherefore watch, remembering that for three years, night and day, I ceased not admonishing each one of you with tears.