What is the ruling on money acquired from selling something that was later discovered to be stolen, and is it permissible to dispose of it if it is unlawful?

It is not permissible to buy or sell stolen property because it belongs to its rightful owners. Whoever knows that something is stolen and still buys it commits a sin. Whoever has bought a stolen item must return it to its owner if the owner is known and can be found. Otherwise, he is responsible for it by returning a similar item or its value. If the owner is not known, he should give it away in charity with the intention of getting rid of unlawful gain. Scholars have stated that stolen property must be returned or guaranteed if it has been damaged.

Therefore, you must return the stolen money to its owners, either by returning the exact item if it is still intact, or by guaranteeing it, and also returning any profit as a precaution. You may then seek reimbursement from the seller for the price you paid.