Leviticus 14:15

And the priest shall take some of the log of oil, and pour it into the palm of his own left hand:

Cross-reference

Leviticus 14:10 lists the log of oil that is poured in verse 15, providing the immediate source for this step in the cleansing ritual.

Exodus 29:21 also uses anointing oil for consecration, here sprinkled on priests—a parallel ritual for setting apart persons to God.