if I paid zakat on my income in 2000 and in the year of 2001 there was no increase in my income; so, the money on which I already paid zakat, do I have to pay zakat again or not?
Yes, as long as there is a nisab (the person owns as much money where he/she would be obligated to pay zakat) at the end of every year zakat has to paid, its wajib. Allah knows best.
Original Source Link (from Way Back Machine archive)