Yes, you're obligated to report the receipt of funds to both Medicaid and Social Security. Your current income has nothing to do with this obligation. Those funds will be considered income in the month received and an asset thereafter.
You will face a dollar-for-dollar reduction in your monthly SSI payment in the month in which you receive the excess income. The SSI program only allows you to keep $2,000 in cash, so you would need to provide the agency with proof that you spent the money on yourself until you reduced the cash to below $2,000. You cannot give the money away, as that would be considered a disqualifying transfer.
You do not say which MassHealth program you receive. There are several different MassHealth programs, each of which has its own rules concerning income and assets. If you are on MassHealth Standard (a/k/a Community MassHealth), there is an income cap but no asset limitation.
You may find it helpful to consult with an elder law attorney for advice specific to your situation.
E. Alexandra "Sasha" Golden is a Massachusetts lawyer. All answers are based on Massachusetts law. All answers are for educational purposes and no attorney-client relationship is formed by providing an answer to a question.