Gold From Egypt?

Where did the Israelite got all the gold and silver mentioned in Bamidbar 7:84-85?

Shalom! 

Thank you for your question. 

The gold came from two episodes: 

The first is that when the Jews left Egypt, they got gold, silver, and all kinds of wealth from their Egyptian neighbors just prior to leaving Egypt. 

As Rashi says on Exodus 12:36: 

“...and they emptied out [Egypt from their wealth] 

This was also foretold in Rashi to Genesis 45:18 as it says: 

“...the best of the land of Egypt: [I.e.,] the land of Goshen. He prophesied but did not know what he was prophesying. They (the Israelites) would eventually make it (Egypt) like the depths of the sea, which have no fish [from taking all their wealth]” 

Furthermore, they got more gold, the gold of the royal treasury, after the splitting of the sea and the drowning of the Egyptians. The gold floated to the top. 

As Rashi says on Exodus 15:22: 

“Moses led Israel away: lit., made Israel journey. He led them away against their will, for the Egyptians had adorned their horses with ornaments of gold, silver, and precious stones, and the Israelites were finding them in the sea. The plunder at the sea was greater than the plunder in Egypt, as it is said: “We will make you rows of gold with studs of silver” (Song of Songs 1:11). Therefore, he had to lead them against their will.” 

I trust that answers the question.