The share purchase agreement, the buyer's payment records, the company's financial statements and corporate registers, the tax filings reporting the disposition, and evidence of how the shares were originally acquired. Then bank statements tracing the proceeds through every account to the US enterprise without gaps.
Prove the sale, then prove the trail
Start further back than feels necessary. The officer will want to know how the seller came to own the shares, so include the incorporation documents, the original share subscription or purchase, and the corporate history that explains any later reorganizations. Then document the sale itself: the executed agreement, closing statement, the buyer's wire confirmations and the seller's bank statement showing receipt.
Add the personal and corporate tax filings that report the transaction, because unexplained differences between the reported gain and the proceeds are a common request-for-evidence trigger. Next, the path: every account the money passed through, including any short-term investment or currency conversion, with statements that overlap in date so no period is unaccounted for. Finally, the transfer to the US enterprise and the enterprise's own statements showing the deposit and its use for equipment, lease and working capital.
Translate nothing unless a document is not in English, and keep the originals available for the consular or adjustment stage.