If a borrower is using commission income for 25% or more of their total income,...

For FHA loans, when a borrower’s commission income is 25% or more of total income, the lender must obtain copies of the borrower’s signed federal income tax returns for the previous two years and must also document current commission income.

“Commission income must be averaged over the previous two years. Borrowers whose commission income represents 25 percent or more of their total annual employment income must provide signed tax returns for the previous two years.”

— HUD 4000.1 FHA Single Family Housing Policy Handbook