Is it permissible to appoint an agent (Wakil) with or without a stipulated fee (Ja'al)?

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The appointment of an agent is permissible whether a fee is stipulated or not. Evidence for this is found in the practice of the Prophet, peace be upon him, who appointed Anis to carry out Hadd punishments, Urwah to purchase a sheep, and 'Amr and Abu Rafi' to accept marriages, all without a stipulated fee. Furthermore, he used to send agents to collect Zakat, granting them a commission (Imalah). This is supported by the request of his two cousins, who asked to be sent to collect Zakat so they could remit what the people remit and receive what the collectors receive, intending the commission.