Mormon 3:14–15

And when they had sworn by all that had been forbidden them by our Lord and Savior Jesus Christ, that they would go up unto their enemies to battle, and avenge themselves of the blood of their brethren, behold the voice of the Lord came unto me saying:

“Vengeance is mine, and I will repay;
and because this people repented not
after I had delivered them, behold,
they shall be cut off from the face of the earth.”

From section: Nephite Revenge and Mormon’s Resignation

From page: Nephite Decline and Downfall