Wilford Woodruff mentions the first endowments for the dead in his journal.
Wilford Woodruff, Journal, January 9, 1877, The Wilford Woodruff Papers
This is the day that the first ordinances of the Endowments for the dead was performed in the Temple of God in St George at 12 oclok President Brigham Young being present we commenced to Baptized fore the dead W. Woodruff Baptized the first 141 persons and confirmed the first persons President Young laying on hands at the same time. John L Smith Baptized the next 83 person making 224 Baptized on this day. John D T. Mcallister confirmed 44 A. H Raleigh 15 H. W. Bigler 124 Erastus Snow 20. Susie Amelia Young Dunford was the first Baptized & confirmed By W Woodruff