20 CFR § 404.750 - Evidence of a parent's support.
If you apply for parent's benefits, we will ask you for evidence to show that you received at least one-half of your support from the insured person in the one-year period before he or she died or became disabled. We may also ask others who know the facts for a signed statement about your sources of support. We will ask you for the following evidence:
(a) The parent's signed statement showing his or her income, any other sources of support, and the amount from each source over the one-year period.