Exodus 32:5

And when Aaron saw it, he built an altar before it; and Aaron made proclamation, and said, To morrow is a feast to the LORD.

And when Aaron saw it,.... In what form it was, and what a figure it made, and how acceptable it was to the Israelites. The Targums of Jonathan and Jerusalem paraphrase it,

"and Aaron saw Hur slain before him;''

for reproving them for their idolatry, as the Midrash {e}, quoted by Jarchi, says: and Aaron fearing they would take away his life if he opposed them,

he built an altar before it; that sacrifice might be offered on it to it:

and Aaron made proclamation, and said, Tomorrow is a feast to the Lord; that is, he gave orders to have it published throughout the camp, there would be solemn sacrifices offered up to the Lord, as represented by this calf, and a feast thereon, which was a public invitation of them to the solemnity: though some think this was a protracting time, and putting the people off till the morrow, who would have been for offering sacrifice immediately, hoping that Moses would come down from the mount before that time, and prevent their idolatry.

{e} So Pirke Eliezer, c. 45.