Received a large (legal) cash inheritance outside of the estate meaning there is no record of it, will I be audited if I put it in a bank?

First we have to figure out if this is even legal, what do you mean "outside" the estate and how then was it given to you. Why and how was this money keep out of the estate?

And when you mean cash, are you talking about actual cash ( 100 dollar bills or so)

And when you say large, are you talking about 3000 dollars, 30,000 dollars or a lot more.
One perhaps "a lot" is not anothers.

I suspect he means that he received a payment that was NOT administered by the estate, such as an insurance settlement.

If any amount over $10,000 is deposited in the bank, the bank will report that deposit to the IRS, who will then come calling to ask from where you got that money. As long as you can show that the disbursement from the other party was legal, you have nothing to worry about.