This can be stated as an indirect quote. Alternate translation: "Then Moses asked Aaron what the people do to him, that he have brought such a great sin on them" (See: [[rc://en/ta/man/translate/figs-quotations]])
Moses spoke of causing people to sin as if sin were an object and Aaron put it on them. Alternate translation: "you have caused them to sin so terribly" (See: [[rc://en/ta/man/translate/figs-metaphor]])