Q: Can we pay off our mortgage with interest money?
A: A mortgage bond may not be paid off with interest money. Interest or usury must be given to the poor or used for the benefit of the general public in amenities such as public toliets and bathrooms, building bridges and roads etc.
It is not even permissible to pay off the interest of a bond with interest money acquired from another financial institute.
However, if one received interest from the same financing house where the mortgage has been taken out, then it will be permissible to use the interest money to pay of that bond, because then you are simply giving back to the company (bank etc) its own money.
And Allah knows best
Mufti Siraj Desai