Exodus 32:6

And on the day following, they arose, and sacrificed burnt-offerings; and the people sat around to eat and to drink, and rose up to disport themselves with strange service.

AND THE PEOPLE SAT DOWN TO EAT AND TO DRINK. This means that they all sat down together to eat and drink inordinately, as they would do at feasts and on festivals, and afterwards they rose up to make merry with their idols and indulge in revelry. Scripture tells us this on account of what Moses [later] said, the noise of them that sing do I hear, for Moses found them acting riotously in front of him and his heart was lifted up in the ways of the Eternal, to take it from before them and to burn it in their presence [and scatter its powder upon the water] and make them drink of it.
Now Scripture first completed the account of everything they had done with the calf, and afterwards told of what the Holy One, blessed be He, said to Moses, Go, get thee down. This communication, however, was given to Moses early that morning, when they worshipped the calf and sacrificed to it. When Moses came down from the mountain they had sat down to eat and to drink, and rose up to make merry, and he found them in revelry. This also is proof to what I have explained [that at first their intent was not to worship idols], since it was not said to Moses, Go, get thee down, for thy people have dealt corruptly on the day that Aaron made the [golden] calf and the altar, [for had they been made for the purpose of idolatry, Moses] would have come down immediately. Instead, it was only when the people sacrificed to it and worshipped it that He told Moses to go down.