Tax deduction declarations require Form No. 121, unique identification numbers, and quarterly reporting for specified incomes. A declaration under section 393(6) must be furnished in Form No. 121, either electronically after verification or in paper form. The payer must assign a unique identification number to each declaration received during every quarter and include the declaration particulars and number in the quarterly tax deduction statement, even if no tax was deducted. The declaration may be required by an income-tax authority within seven years from the end of the relevant tax year for verification or proceedings.