Is zakat obligatory on money saved to buy a house, especially if the zakat payer will be penalized twice by paying rent and zakat?

Zakat is obligatory on money saved for purchasing a home if it reaches the nisab and a full year has passed over it. It is an obligation that purifies wealth and makes it grow, not a punishment. It is not permissible to borrow with interest to buy a home if renting is possible, for usury is deprived of blessing in this world and warrants punishment in the Hereafter.