The unnamed source Moroni cites as he closes the Nephite record. Writing alone after the destruction of his people, Moroni introduces the words with “Behold what the scripture says,” attributing them to a prior text rather than to himself; the author of that scripture is not identified (Mormon 8:20).
The quoted words reserve judgment and vengeance to God: “man shall not smite, neither shall he judge; for judgment is mine, saith the Lord, and vengeance is mine also, and I will repay” (Mormon 8:20). The passage continues that whoever breathes out wrath and strifes against the work of the Lord and against his covenant people, the house of Israel, and says “We will destroy the work of the Lord,” is “in danger to be hewn down and cast into the fire” (Mormon 8:21).