Everything that explains how the money was lawfully earned and everything that shows where it went: business sale documents, closing statements, tax filings, loan agreements and security instruments, property ownership records, and consecutive bank statements for each account the funds pass through.
Build it forward from the origin, not backward from the wire
Families that start at the wire and work backwards find gaps they cannot fill, because the records they need are years old and sit with an accountant or a bank that no longer holds them. Starting at the origin is easier: begin with the business that generated the money, gather its financial statements and tax filings for the relevant years, then the sale agreement and closing statement, then the account that received the proceeds. Follow the money forward, account by account, keeping consecutive statements rather than selected pages. Where funds were commingled with ordinary household money, explain the commingling rather than hoping it goes unnoticed. For the borrowed portion, include the loan agreement, the security instrument, proof of ownership and current value of the pledged home, and evidence the advance was actually received.
Hypothetical example: a precision-map printing business was sold years ago and proceeds later entered several accounts. The review should decide how to document every movement from lawful origin to investment, using tax returns, sale documents, closing statement, and consecutive account records. Build an exhibit list naming what each item proves and where its date appears. Obtain a replacement or explanation while the source is available. The common error is that an affidavit rarely replaces a missing contemporaneous transfer record. Reconcile names, dates, amounts, and role descriptions before reliance.