Brigham Young teaches that Cain and Abel's Heavenly Grandfather (Adam's Father) promising not to kill Cain after he murdered his brother.
Brigham Young, Speech before Territorial Legislature, February 5, 1852
Cain became <jealous> of him, and he laid a plan to obtain all his flocks, for through his perfect obedience to father he obtained more blessings than Cain. Consequently he took it into his heart to put able able of this mortal existence. After the deed was done, the Lord enquired for able, and made Caine own what he had done with him. Now says the grand father I will not distroy the seed of michael and his wife, and Cain I will not kill you, nor suffer any one else to kill you . . .