What is the ruling of Islamic law on the earnings from the sharing economy, where a participant sends a sum of money to a company, which then uses it to purchase a device and lease it out, subsequently sending the participant a specific daily amount five days a week for a year, and at the end of the year returns 80% of the original amount while ownership of the device remains with the company?

It is permissible to purchase a permissible device and appoint someone to buy and rent it out, provided that the profit is a known percentage of the income, not a fixed amount. The majority of scholars view this arrangement (giving a device to someone to work with on a profit-sharing basis) as impermissible, while the Hanbalis permit it by analogy with mudarabah (definition) (profit-sharing partnership) and musaqat (irrigation partnership).

It is permissible for the company to rent the device from its owner for a specified amount and then rent it out to people. However, if the company is a partner, it is not permissible to allocate a fixed amount to the device owner.

Upon termination of the contract, the device returns to its owner. It is not permissible for the company to guarantee the client 80% of the device's price, because guaranteeing capital invalidates the partnership. A promise to purchase the device at its price at the time of sale is permissible, but not a guarantee of a specific amount. Furthermore, it is not permissible to make the sale of the device contingent on a condition (like the end of the term), because such conditions are invalid in a sale.

One must be cautious of transactions involving falsehood or deception, especially online.