Is this partnership, in which employees pay 60% of the profits after covering costs and rent, and the employer takes 40%, with the employer reimbursing the rent previously paid by the employees at the end of the year, legitimate in Islam?

Scholars differed on the permissibility of the wage being a percentage of the profit. The majority of scholars prohibit it because the wage is unknown, citing the Prophet's (peace be upon him) prohibition of hiring a worker until his wage is known. However, the Hanbalis consider it permissible by analogy with musaqat (sharecropping in irrigating) and muzara'ah (sharecropping in cultivation). Ibn al-Qayyim views it as a form of partnership, not ijarah (leasing/hiring), and Ahmad explicitly stated this.