If you received $10,000 or more in one or more related transactions you must file Form 8300

Each person engaged in a trade or business who, in the course of that trade or business, receives more than $10,000 in cash in one transaction or in two or more related transactions, must file Form 8300. Any transactions conducted between a payer (or its agent) and the recipient in a 24-hour period are related transactions. Transactions are considered related even if they occur over a period of more than 24 hours if the recipient knows, or has reason to know, that each transaction is one of a series of connected transactions.