Though Moses claims God was angry at Aaron for his role in the Golden Calf episode, Aaron is never punished for idolotry
In this week's portion, Ekev, Moses continues his farewell address to the people of Israel. He begins by describing the blessings that will accrue if the people observe God's laws (fertility, health, military dominance) and the miraculous means by which God will allow them to conquer the land of Israel. Moses exhorts them to remember the lessons of the wilderness, that God is the source of their good fortune, so they do not mistakenly conclude that "My strength and the power of my hands have created this wealth for me" (Deuteronomy 8:17). Moses chides the Israelites for their prior rebellions against God, reminding them of the sin of the Golden Calf and of the spies. The portion concludes with further adjurations to keep God's laws and so merit continued residence in the Land of Israel.
In the course of his admonishments, Moses retells in detail the sin of the Golden Calf. Most of the story is familiar from Exodus 32. Moses describes how, while he was on the mountaintop receiving the Tablets of the Law, God told him to descend because the people had sinned. Moses relates how he prayed for forgiveness for the people and then shattered the tablets himself upon personally witnessing the people's decay. One fascinating new fact is added to the Deuteronomy account of the sin. Moses explains, "And at Aaron, God was very angry to have destroyed him, and I also prayed on Aaron's behalf at this time" (Deuteronomy 9:20). This verse reopens the question of Aaron's participation in the sin.