Is it permissible to give money to a friend who works in contracting, on the condition that he returns a profit ranging from 35 to 40%?

There is no harm in giving money to a friend to invest it in contracting, in exchange for a known percentage of the profit, provided that the conditions of mudarabah (profit-sharing) are observed. However, specifying the percentage as being between 35% and 40% is not permissible; rather, a known percentage must be specified and applied to the profit, not to the capital. This is because applying the percentage to the capital is considered a guarantee of a known amount, which is not permissible in a mudarabah contract. Scholars have unanimously agreed on the invalidity of qirad (another term for mudarabah) if one or both parties stipulate a fixed number of dirhams for themselves.