The verse says...

The verse says: “And when they smote their hands and saw that they had gone astray, they said: ‘Should our Lord have not mercy on us and forgive us (not), we shall certainly be of the losers’,” Some of the commentators believe that Sāmeri, with the information he had, had set some special pipes in the breast of a golden calf through which some pressed air could pass out and a sound, similar to the sound of a cow, was heard from the mouth of that calf.

“And when Moses returned (from the Mountain) unto his people, wrathful (and) grieved, he said: ‘Evil it is that you have done in my place after me. Did you hasten on the bidding of your Lord?’ And, he dropped the Tablets and seized his brother by the head, dragging him toward himself. He (Aaron) said: ‘O son of my mother! verily the people judged me weak and had well-nigh slain me.

So do not let the enemies gloat over me, and do not count me among the unjust people.” In this verse and the verse after it, the event of the conflict of Moses (as) with calf-worshippers, when he returned from the tryst, has been explained. This event was only hinted out in the previous verse. This is an explanation upon the hideous and hateful scene of the calf-worshipping of the people of Moses who had spoilt his religion when Moses came back from the Mountain.

The verse says: “And when Moses returned (from the Mountain) unto his people, wrathful (and) grieved, he said: ‘Evil it is that you have done in my place after me…” Then, Moses (as) added telling them: “…Did you hasten on the bidding of your Lord?’…” The objective meaning of this phrase is that, due to the command of Allah concerning the length of the appointment of Moses (as) from thirty nights to forty nights, the people of Moses hastened and judged over it hurriedly.

They took the absence of Moses (as) as a reason for his death or breach of promises. In that circumstance, Moses had to manifest an intensive wrath, otherwise their return to the truth was not easily possible.