What is the ruling on one who takes from money designated for zakat al-mal with the intention of returning it later, knowing that he pays his zakat in installments throughout the year?

The question is ambiguous, but if the owner of wealth sets aside the amount of zakat, this isolated money is not designated for zakat, and he may disburse other money instead. Therefore, there is no blame upon him for taking the isolated money and spending it. Zakat must be disbursed immediately when it becomes due, whether a specific amount has been allocated for it or not.