Acts 20:28-31

28 Take heed, therefore, to yourselves, and to all the flock, in which the Holy Spirit has made you overseers, to shepherd the assembly of the Lord and God which he purchased with his own blood.  29 For I know that after my departure, vicious wolves will enter in among you, not sparing the flock.  30 Men will arise from among your own selves, speaking perverse things, to draw away the disciples after them.  31 Therefore watch, remembering that for a period of three years I didn't cease to admonish everyone night and day with tears.