Sunan Ibn Majah, Chapter: The Book of the Sunnah

that the Messenger of Allah (saw) said: "Every caller who invites people to misguidance and is followed, will have a burden of sin equal to that of those who follow him, without that detracting from their burden in the slightest. And every caller who invites people to true guidance and is followed, will have a reward equal to that of those who follow him, without that detracting from their reward in the slightest.'" (Hasan)