No, you do not report mortgage down-payment assistance on your tax return. It is not taxable income.
From IRS Publication 525 (2015), Taxable and Nontaxable Income:
Down payment assistance. If you purchase a home and receive assistance from a nonprofit corporation to make the down payment, that assistance is not included in your income. If the corporation qualifies as a tax-exempt charitable organization, the assistance is treated as a gift and is included in your basis of the house. If the corporation does not qualify, the assistance is treated as a rebate or reduction of the purchase price and is not included in your basis.
