Admissibility of prayers in a dwelling purchased on interest accruing mortgage plan.

According to our understanding of your question, you are in partnership with someone and together you have bought a house on an interest based mortgage plan. In addition to this, you share expenses.

Regardless of who is paying the instalment for the house, you are the owner of a part of it and he is paying on your behalf, thus, you are actually paying interest. This is completely Haraam and draws the curse of Allah. You should immediately look for an alternative method of financing. However, buying a house in this manner will not result in your staying in the house being sinful, neither will it effect the acceptability of prayers, etc. In short, paying the interest is a sin. However, it will not make the house Haraam.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai