Wilford Woodruff (in 1889) denies there being an oath to avenge Joseph and Hyrum Smith's deaths in the endowment.
"President Woodruff Speaks," interview dated November 22, 1889 in Deseret News 39 no. 24 (December 7, 1889): 1
President Woodruff—I have already said that there is nothing of that kind in any part of phrase of "Mormonism." I ought to know about that as I am one of the oldest members of the Church. A good deal is being made of a form of prayer based upon two verses in the sixth chapter of the Revelations of St. John, as contained in the New Testament. It relates to praying that God might avenge the blood of the prophets. An attempt has, I see, been made to connect this with avening the death of Joseph and Hyrum Smith, and to have reference to this nation. It can have no such application, as the Endowments were given long before the death of Joseph and Hyrum Smith, and have not been changed. This nation or government has never been charged by the "Mormon" people with the assassination of Joseph and Hyrum Smith, as it is well known the murder was the act of a local mob disguised.
Reporter—Then there is nothing in the cry about blood atonement?
Presidnet Woodruff: Well, there is this: The foundatoin of our religious faith is belief in the atoning blood of Christ, through which the resurrection will be brought about. We believe in the scriptural doctrine, whoso sheddeth man's blood by man shall his blood be shed; but we also believe that all executions for murder should be under the law of the land and by its officers only.