Is a general power of attorney permissible, or is a specific power of attorney required; and is an informal power of attorney permissible, or is a formal power of attorney stipulated?

Agency (Al-Wakalah (definition)) is permissible according to the Qur’an, Sunnah (definition), and scholarly consensus. It means delegating an action to another. There is no disagreement regarding the permissibility of a special agency (Al-Wakalah Al-Khasah). However, for a general agency (Al-Wakalah Al-Ammah), there is a difference of opinion among scholars regarding its validity and acceptance. The Hanafis and Malikis consider general agency permissible, while the Shafi’is and Hanbalis deem it invalid. It is preferable for agency to be special rather than general, to avoid disagreement. Customary agency is valid.