All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.

It is permissible for a partner to rent his share to his other partner against a fixed monthly payment so long as the former has complete ownership of that share. This is because such a transaction does not violate the provisions of Sharia.

"Rent of joint property is permissible since personal and joint property have the same rulings in terms of selling and renting." [Al-Muhathab], A Shafie book. Moreover, it is stated in [DkaekOulaAlnha], a Hanbali book," It is permissible for the partner to rent his partner's share or to rent their property for the same person."

Therefore, it is permitted for one of the partners to rent his share to his other partner. And Allah knows best.