A cash basis taxpayer who owns a sole proprietorship company has an income in 2017 - say $50,000. He deposited the income in the sole proprietorship's bank account, he guarantees that people who met the criteria he mentioned will get a full refund. He wouldn't know who would qualify for a refund until next year - 2018. Should he include the revenue on his 2017 or 2018 gross income? And why?

- please include cites or . thank you