Is it permissible to delay giving the Zakat on money—which reached the nisab after one year from receiving its first installment—until the last ten days of Ramadan, in order to increase the reward and to set a fixed annual date for Zakat?

If a year has passed on wealth that has reached the [minimum] nisab (definition) threshold, it is obligatory to promptly disburse the zakat (definition) immediately. It is not permissible to delay it without a valid excuse, and waiting for Ramadan (definition) is not a permissible excuse for delay. Thus, delaying zakat after it becomes due is a sin and an act of disobedience, and there is no reward in it. It is possible to pay zakat in advance, before the year is complete, in order to disburse it in Ramadan.