He harms himself who does harm to another, and the evil plan is most harmful to the planner.
οἷ γ᾽ αὐτῷ κακὰ τεύχει ἀνὴρ ἄλλῳ κακὰ τεύχων
ἡ δὲ κακὴ βουλὴ τῷ βουλεύσαντι κακίστη.
ἡ δὲ κακὴ βουλὴ τῷ βουλεύσαντι κακίστη.
Original text (Ancient Greek)
Notes from Wikiquote
He for himself weaves woe who weaves for others woe,
and evil counsel recoils on the counsellor. | Lines 265–266