I am giving one house/shop building for rent. It is normal in our country to charge the rent monthly and also get a lump sum deposit for a year or two on the basis of rent to be returned at end of the contract period.
Is this lumb sum retention allowed in Shariah

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

This transaction is permissible on the condition that the mortgagee (landlord) should not benefit from the amount of mortgage by investing it and the like except with the permission of the tenant. This is because the amount that the tenant pays is a security deposit for renting the house in a way that the landlord takes from it the rent that the tenant refuses to pay. Ibn Qudaamah said: “What does not need expenses like a house, personal property and the like, then it is not permissible at all for the mortgagee to benefit from it without the permission of the mortgager and we do not know any difference of opinion about this.”

In another place, he [Ibn Qudaamah] said: “If the mortgage is the same as the price of a sold item or a rent of a house, or a debt other than a loan, and the mortgager gave him permission to benefit from it, then this is permissible.”   

Allaah Knows best.