Sforno on Exodus 32:35/ספורנו על שמות ל״ב:ל״ה

1על אשר עשו את העגל אשר עשה אהרן, by Aaron’s agreeing, not protesting, he helped a potential sin become an actual sin, so that the person’s sin who fashioned the gold into the shape of a calf is attributable to Aaron. Aaron’s contribution in deed was his throwing the gold into the fire. He himself describes the “this calf emerged,” as a direct consequence of his throwing the gold into the fire (verse 24).