This Is The Word Of Yahweh (Leviticus 13:1).
‘And Yahweh spoke to Moses and to Aaron, saying,'
Here Aaron is for the second time included with Moses in receiving the word of Yahweh (compare Leviticus 11:1), and will be again in Leviticus 14:33 and Leviticus 15:1. This suggests that at times he approached Yahweh in Moses' company, although never as the prime person. In spite of his status he could not outrank Moses. But here he was present as a witness to what God said. Judging by the Book of Numbers, where Aaron is not conjoined with Moses in this way until after the confirmation of Aaron's position in Numbers 18, it was prior to the arrival in Kadesh.