Mining
Coinbase outputs.
Mining rewards are documented via mining pool statements (Foundry, Antpool, F2Pool, etc.) plus hash-rate evidence (electricity bills, hardware invoices) showing the operation existed. Solo miners document the pool-equivalent: the block templates, the hash-rate-on-network share, and the coinbase outputs at the addresses you control.
Payment received
Invoices & contracts.
If you accepted Bitcoin for services rendered (freelancers, agencies, advisory work), the file is your invoice, the engagement contract, and the on-chain payment matching the invoiced amount. Multiple small payments aggregate cleanly via wallet history; the VFIU accepts a payment ledger keyed to invoices.
Pre-coinbase & early holdings
Historical purchases.
For Bitcoin acquired before exchange records existed (Mt. Gox, early peer-to-peer, faucet, etc.), the file is reconstructed from the on-chain history, bank wires that funded the original purchase if available, and a signed affidavit attesting to the acquisition. The VFIU accepts this combination for pre-2014 holdings; later holdings need a stronger paper trail.