John Gill Commentary Leviticus 15:1

"And Jehovah spake unto Moses and to Aaron, saying," — Leviticus 15:1 (ASV)

And the Lord spoke to Moses, and to Aaron
Aaron is spoken to as well Moses, because some of these purifications, afterwards mentioned, depended on the priest, as the affair of profluvious men and women, as Gersom observes:

saying ;
as follows.