Keep a song in your heart.
Murder is forbidden by the commandments of God. It's in the Bible, Deuteronomy 5:17, TLB. "You must not murder."
Anger can be a form of murder. It's in the Bible, Matthew 5:21-22, NIV. "You have heard that it was said to the people long ago, 'Do not murder, and anyone who murders will be subject to judgment. But I tell you that anyone who is angry with his brother will be subject to judgment."