What distinguishes the specifically hired laborer (Al-Ajir Al-Khas) from the jointly hired laborer (Al-Ajir Al-Mushtarak)?

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The specifically hired laborer is defined as one whose contract covers a known duration, during which the hirer has exclusive right to his service, such as a man hired for general service, construction, tailoring, or caretaking for a day or a month. He is termed 'specific' because the hirer exclusively possesses his benefit for that period, to the exclusion of others. The jointly hired laborer is one contracted for a specific act, or for a period where the hirer does not possess all of his benefit, as he can work for multiple clients simultaneously, sharing his benefit among them.