Deuteronomy 9:21

“And I took your sin, the calf which ye had made, etc.] Which was the object of their sin, which lay in making and worshipping it; (see <233107> Isaiah 31:7) and burnt it with fire, and stamped it; with his feet after it was burnt, to bring it into small pieces: and ground it very small; or, as the Targum of Jonathan, “ground it in a mortar well;” the burnt and broken pieces: even until it was as small as dust; being ground to powder, as in (<023220>Exodus 32:20) and I cast the dust thereof into the brook that descended out of the mount; and made the children of Israel to drink of it, as in the previously mentioned place; (see Gill on “<023202>Exodus 32:2”); all this was done before the…”

“I cast the dust thereof into the brook that descended out of the mount--that is, "the smitten rock" (El Leja) which was probably contiguous to, or a part of, Sinai. It is too seldom borne in mind that though the Israelites were supplied with water from this rock when they were stationed at Rephidim (Wady Feiran), there is nothing in the Scripture narrative which should lead us to suppose that the rock was in the immediate neighborhood of that place (see on Exo 17:5). The water on this smitten rock was probably the brook that descended from the mount. The water may have flowed at the distance of many miles from the rock, as the winter torrents do now through the wadies of Arabia-PetrÃ&brvbra…”

“Into the brook - That there might be no monument or remembrance of it left. Deuteronomy 9:25”

“I took: Exo 32:20; Isa 2:18-21, Isa 30:22, Isa 31:7; Hos 8:11 the brook: This was the stream which flowed from the rock that Moses smote with his rod ( Exo 17:6), and to which the Psalmist alludes in Psa 78:16-20; Psa 105:41. Philo relates, that upon Moses' striking the rock, the water poured out like a torrent, affording not only a sufficient quantity for allaying their present thirst, but to fill their water vessels, to carry with them on their journey. Deuteronomy 9:22”