The verse says...

The verse says: “They said: ‘Never will We cease worshipping it, until Moses returns unto us’.” Thus, they refused both the firm order of intellect, and the command of the successor of their Divine leader. But in any case, Aaron accompanied with a minority of the true believer, who were about ten thousand persons, separated from that community, while a majority of them, who were ignorant and obstinate, wanted to kill him.

“(Moses) said: ‘O Aaron! What hindered you when you saw them going astray,” 93. “So that you did not follow me? Did you then disobey my order?’” 94. “Said (Aaron): ‘O son of my mother! Seize me neither by my beard nor by (the hair of) my head!

Verily I feared lest you would say ‘You have caused division among the Children of Israel, and you did not observe my word!’” When Moses (as) returned from Tur (Mount Sinaie) and found his people misguided, he interrogated three types of people: His people, whom he asked: “Did not your Lord promise you a fair promise (the descent of the Turah)?” [^1] Aaron, to whom he said: “What hindered you…?” Samiri, whom Moses addressed and said: “What then was your object, O Samiri?” As it is recorded in Atyab-ul-Bayan, the commentary, since Aaron was a prophet and was sinless, he had done his duty of enjoining good and forbidding evil.

Therefore, the action of Moses (as) against Aaron can idiomatically be rendered into a ‘sham quarrel’, or he says: ‘If the cap fits, wear it’, and he addresses Aaron so that people might be careful of their own accountability. But, there is a tradition recorded in At-Tafsir-us-Safi, narrated from Imam Sadiq (as), which says that the reprimand of Moses (as) was this that why Aaron (as) did not immediately inform Moses of that circumstance when he saw it.