All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The condition for the validity of the Mudhaarabah contract is that the profit is divided between the two parties according to a ratio, one-third or one-fourth or one-half, for example. If a known fixed amount is guaranteed as a profit share for either of them, then the Mudhaarabah contract becomes invalid. Therefore, it is impermissible to give the agent (Mudhaarib) a share of the capital in return for his services and effort because that share would mean guaranteeing a known fixed amount of profit for him whereas his share should be a ratio of the profit, if a profit is made.
Ibn Qudaamah said in his book Al-Mughni: "It is impermissible to stipulate a fixed amount of money to any of the partners. In brief, if a fixed amount is stipulated to any of the partners as a profit share, like a number of Dirhams for instance, or it is stipulated that he gets a ratio of the profit plus a fixed number of Dirhams, then the Mudhaarabah contract is invalid. Ibn Al-Munthir said: 'All scholars from whom knowledge is to be taken have agreed by consensus that Mudhaarabah is invalid if either or both partners stipulate for himself a fixed number of Dirhams.'"
Allaah Knows best.