Is it permissible, Islamically, to mortgage a house in exchange for paying one million in advance for three years, along with a monthly payment of four thousand?

The question is unclear, but if what is meant is mortgaging a house to pay off a loan, then there is no objection to it, provided that the creditor does not benefit from the house, because it would then become a loan that draws a benefit, which is forbidden. However, if what is meant is paying an amount as a security deposit when renting a house, then there is no harm in it, provided that the mortgagee does not benefit from the amount except with the permission of the mortgagor, as stated in Al-Mughni by Ibn Qudamah.