A document for every component and every transfer: sale agreements, closing statements, gift instruments with the donor's own evidence, plan withdrawals, tax filings and account statements covering the whole path.
A chain that must not break anywhere
For proceeds from selling a business, produce the share or asset purchase agreement, the closing statement, the accountant's calculation and the deposit into a named account, together with corporate tax filings for the years in which the business earned the money. For a gift, produce a signed gift instrument, evidence of how the donor lawfully acquired the funds, and the transfer record; a gift letter without the donor's financial history leaves a gap in the lawful-source evidence. For a withdrawal from a registered plan, produce the plan statements, the withdrawal confirmation and the tax slip. Then supply consecutive statements for each account the money touched, including the currency conversion, so that the totals reconcile exactly. Add personal tax filings for the relevant years, because they corroborate the story the other documents tell.
Hypothetical example: a reclaimed-brick manufacturer will fund an investment from a business sale, a secured loan, and dividends accumulated over several years. The first review should make a chronological ledger from original ownership through sale documents, loan security, tax reporting, account statements, and the eventual transfer. The closing statement and loan documents settle separate sources; consecutive bank records show the path. Obtain gaps before filing. The frequent error is presenting the beginning and ending balances only, leaving unexplained movements that prevent a reviewer from tracing the claimed capital.