Is zakat due on the principal amount deposited in the Egyptian Post from which a monthly pension is disbursed, which is the sole source of income, or is zakat due on the pension that is disbursed from it, knowing that taking from the principal amount leads to a reduction in the pension?

You must withdraw from usurious transactions and dispose of the interest by giving it to the poor and needy or spending it on the welfare of Muslims. As for the principal, Zakat (definition) is obligatory on it if it reaches the nisab (definition), which is equivalent to 85 grams of gold or 595 grams of silver, and the amount of Zakat that must be given is 2.5% (a quarter of a tenth).