Russell M. Nelson comments on temple rites being of ancient origin.
Russell M. Nelson, "Becoming exemplary Latter-day Saints," Conference Report, October 2018, accessed October 26, 2021
Consider the great mercy and fairness of God, who, before the foundation of the world, provided a way to give temple blessings to those who died without a knowledge of the gospel. These sacred temple rites are ancient. To me that antiquity is thrilling and another evidence of their authenticity.
The footnote attached to this comment by President Nelson refers to Exodus 28; 29; Leviticus 8.