Is the appointment of an agent (Wakalah) legally permissible?

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The appointment of an agent is permissible based upon the Book (Quran), the Sunnah, and scholarly consensus (Ijma). Pertaining to the Book, the statement of Allah the Almighty: "The alms are only to be distributed among the poor and the needy, and those who collect them..." (Quran 9:60) permits acting on behalf of others, which establishes agency through substitution for the rightful recipients. Furthermore, the verse, "So send one of you with this silver coin of yours to the city, and let him look to which of them has the purest food and bring you provision from it..." (Quran 18:19) demonstrates an act of agency (Wakalah). As for the Sunnah, Al-Athram, Abu Dawud, and Ibn Majah narrated that Al-Zubayr ibn Al-Kharrit reported from ‘Urwah ibn Al-Ja‘d that he presented livestock to the Prophet, peace be upon him. The Prophet gave him one Dinar and commanded him, "O ‘Urwah, go to the livestock market and buy us a sheep with it." ‘Urwah bought two sheep and subsequently sold one for the same Dinar. When he returned with the Dinar and one sheep, and recounted the events, the Prophet supplicated, "O Allah, bless the transaction of his right hand." Additionally, Abu Dawud narrated that Jabir ibn Abdullah reported that when he intended to travel to Khaybar, the Prophet commanded him, "Go to my agent and take fifteen Sa' of dates from him; if he asks you for a sign, place your hand upon his collarbone." The Prophet, peace be upon him, also appointed ‘Amr ibn Umayyah Al-Dhamri to accept the marriage of Umm Habibah, and Abu Rafi‘ to accept the marriage of Maymunah.