(a) In general. The credit for taxes provided in subpart A (section 901 and following), part III, subchapter N, chapter 1 of the Code, may ordinarily be taken either in the return for the year in which the taxes accrued or in which the taxes were paid, dependent upon whether the accounts of the taxpayer are kept and his returns filed using an accrual method or using the cash receipts and disbursements method. Section 905(a) allows the taxpayer, at his option and irrespective of the method of accounting employed in keeping his books, to take such credit for taxes as may be allowable in the return for the year in which the taxes accrued. An election thus made under section 905(a) (or under the corresponding provisions of prior internal revenue laws) must be followed in returns for all subsequent years, and no portion of any such taxes accrued in a year in which a credit is claimed will be allowed as a deduction from gross income in any year. See also Sec. 1.905-4.
(b) Foreign income subject to exchange controls. If, however, under the provisions of the regulations under section 461, an amount otherwise constituting gross income for the taxable year from sources without the United States is, owing to monetary, exchange, or other restrictions imposed by a foreign country, not includible in gross income of the taxpayer for such year, the credit for income taxes imposed by such foreign country with respect to such amount shall be taken proportionately in any subsequent taxable year in which such amount or portion thereof is includible in gross income.