Deuteronomy 13:4-5

13:4 You must follow the Lord your God and revere only him; and you must observe his commandments, obey him, serve him, and remain loyal to him. 13:5 As for that prophet or dreamer, ¹  he must be executed because he encouraged rebellion against the Lord your God who brought you from the land of Egypt, redeeming you from that place of slavery, and because he has tried to entice you from the way the Lord your God has commanded you to go. In this way you must purge out evil from within. ² 

[13:5]  ¹ tn Heb “or dreamer of dreams.” See note on this expression in v. 1.

[13:5]  ² tn Heb “your midst” (so NAB, NRSV). The severity of the judgment here (i.e., capital punishment) is because of the severity of the sin, namely, high treason against the Great King. Idolatry is a violation of the first two commandments (Deut 5:6-10) as well as the spirit and intent of the Shema (Deut 6:4-5).