Ruling on discounts if instalments are paid before they are due
Question

                The custom in local schools is that instalments are paid in two parts, before the beginning of the first semester and before the beginning of the second semester. Some schools write to parents and guardians before school begins, saying that if they pay both instalments together before the school year begins, they will get a discount of such and such percent. Is this permissible according to Islam?.
Praise be to Allah.
    There is nothing wrong with that according to the more 
    correct of the two scholarly opinions, because that serves an obvious 
    interest for both parties. And Allah is the source of strength. End quote.