Is it permissible to enter into a business partnership for a specified period, such that a monthly percentage of the profits is paid commensurate with the capital invested, and a portion of the capital is gradually repaid each month with the profit percentage changing based on the remaining capital, until the end of the agreed-upon period?

For the validity of Mudarabah (profit-sharing partnership) and partnerships in general, three conditions are required: knowledge of the investment field and that it is permissible, non-guarantee of the capital except in cases of negligence or dereliction, and that the profit be a known, common percentage of the profit, not of the capital.

If the intention of the Mudarabah is that your profit be 30% of the profit of a specific merchandise valued at 300,0, then that is permissible if the merchandise is known and distinct, and it is inventoried monthly to ascertain the profit.

However, if the merchandise is mixed with the shop's merchandise, this is not permissible, and you must have a percentage of the entire shop's profit. Estimating profit based on capital instead of the actual profit of the trade is not permissible.

The profit must be determined after knowing your capital and the shop's capital upon entering the partnership through a real inventory of the merchandise, followed by an inventory of all merchandise when calculating the profit (annually, or every six months, or monthly). Whatever exceeds the capital is the profit that is to be divided between you. Offering a fixed amount or an approximate percentage of the profit is forbidden.