Ulangan 18:20

18:20 “But if any prophet presumes to speak anything in my name that I have not authorized ¹  him to speak, or speaks in the name of other gods, that prophet must die.

Zakharia 13:3

13:3 Then, if anyone prophesies in spite of this, his father and mother to whom he was born will say to him, ‘You cannot live, for you lie in the name of the Lord.’ Then his father and mother to whom he was born will run him through with a sword when he prophesies. ² 

[18:20]  ¹ tn Or “commanded” (so KJV, NAB, NIV, NRSV).

[13:3]  ² sn Death (in this case being run…through with a sword) was the penalty required in the OT for prophesying falsely (Deut 13:6-11; 18:20-22).