In Mormonism, the oath of vengeance (or law of vengeance) was part of the endowment ritual of the Church of Jesus Christ of Latter-day Saints (LDS Church). Participants swore an oath to pray for God to avenge the blood of prophets; although never specified in the oath, many believe that the "prophets" referenced were Joseph Smith and Hyrum Smith, who were assassinated in 1844. The oath was part of the ceremony until the early 1930s.
The officiant of the ritual is alleged to have enjoined the participants as follows: "You and each of you do covenant and promise that you will pray and never cease to pray to Almighty God to avenge the blood of the prophets upon this nation, and that you will teach the same to your children and to your children's children unto the third and fourth generation."[1]