Is it permissible to purchase an apartment through Murabaha financing via an Islamic bank if the tenant already occupies it and the owner agrees to this arrangement? And is it permissible for the tenant to reclaim the amount paid in advance in the lease contract?

It is permissible to purchase a house or similar property through a Murabaha sale. Similarly, it is permissible for the lessor to sell the leased property without the lease being terminated, whether he sells it to the lessee or to someone else. Accordingly, the lessor owns the upfront rent as it is part of the due rent, and the lessee owns the usufruct for this period. Thus, he may lease it to another person or transfer it to the new owner, with or without compensation.