3 Nephi 6:28

and they did enter into a covenant one with another, yea, even into that covenant which was given by them of old, which covenant was given and administered by the Devil, to combine against all righteousness;

They made a promise to each other. They made the same promise that had been made long ago. This promise was given by the devil. It was to join together against all that is right.

They made a covenant with each other—the same ancient covenant that had been given and managed by the devil, designed to oppose everything good.