Per IRS Publication 17 Your Federal Income Tax For Individuals, on page 68:
A recovery is a return of an amount you deducted or took a credit for in an earlier year. The most common recoveries are refunds, reimbursements, and rebates of deductions itemized on Schedule A (Form 1040). You may also have recoveries of nonitemized deductions (such as payments on previously deducted bad debts) and recoveries of items for which you previously claimed a tax credit.
Tax benefit rule. You must include a recovery in your income in the year you receive it up to the amount by which the deduction or credit you took for the recovered amount reduced your tax in the earlier year. For this purpose, any increase to an amount carried over to the current year that resulted from the deduction or credit is considered to have reduced your tax in the earlier year. For more information, see Pub. 525.
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