Mkataba wa kuajiri au ajira ambao unahusu manufaa ya kazi na manufaa ya mtu ndio ule unaomhusu mfanyakazi. Mfanyakazi ni yule anayejiajiri mwenyewe. Shari'a imeruhusu kumwajiri binadamu kwa ajili ya manufaa yatokanayo naye kama huduma na mfano wake, au manufaa yatokanayo na kazi yake kama uchoraji, upakaji rangi, uhandisi na mfano wake. Ili mkataba wa kuajiri ufanyike, uwezo wa wahusika wawili ni sharti la kufungwa kwake, kwa maana kila mmoja wa wawili hao awe mwenye akili timamu na mwenye busara. Kuajiri kwa mtu mwenye wazimu hakufungiki, wala kuajiri kwa mtoto asiyebaleghe. Ikiwa mkataba wa kuajiri umefungwa, ridhaa ya wahusika wawili ni sharti la uhalali wake, na kile kinachoafikiwa – ambacho ni manufaa – kinapaswa kujulikana kwa namna inayozuia mzozo. Ujuzi huu wa huduma, kwa upande wa mfanyakazi, wakati mwingine ni kwa kuelezea muda, wakati mwingine kwa kupunguza manufaa, au kwa kueleza kwa kina kazi inayohitajika na kubainisha atakachokifanya mfanyakazi au kubainisha jinsi atakavyofanya kazi. Kwa hiyo, kumwajiri mtu aliyelazimishwa si halali, wala kuajiri kwa manufaa yasiyojulikana si halali.

The contract of hiring or employment which came upon the benefit of work and the benefit of the person is the one which relates to the employee. The employee is one who hires himself. The Shar’a has permitted the hiring of the human being for a benefit resulting from him like service and the like or the benefit resulting from his work like painting, dyeing, engineering and the like. In order to contract the hiring, the fitness of the two contractors is a condition for its contracting such that each of the two should be sane and possessing discretion. The hiring of the insane is not contracted, nor the hiring of an immature child. If the hiring contracts, the consent of the two contractors is a condition of its validity, and that which is contracted upon— which is the benefit—be known in a way that prevents dispute. This knowledge of the service, in relation to the employee, at times is by explaining the period, at times by limiting the benefit or describing the required work in a detailed description and specifying what the employee will do or specifying how he will work. Accordingly, hiring the compelled person is not valid nor is the hiring of an unknown benefit valid.