What are the acts of worship in which agency is permissible, and those in which it is not?

Scholars have divided acts of worship into three categories:

1. A category concerning which there is consensus on the validity of deputization: This includes acts whose benefit does not depend directly on the doer's action, such as returning usurped property and paying expenses. 2. A category concerning which there is consensus on the invalidity of deputization: These are acts whose performance is valid only when carried out by the one commanded to do them, such as belief in Allah and monotheism, and prayer according to the majority of scholars. 3. A category concerning which there is disagreement: This includes four issues: Zakat (definition): Is it sufficient if someone pays it without the knowledge or permission of the one upon whom it is due? Hajj on behalf of another: Malik prohibited it, while Al-Shafi'i permitted it. Fasting on behalf of a deceased person who was remiss in making up missed fasts: Ahmad and the Shafi'is permitted it, while Malik prohibited it. Emancipating a slave on behalf of another person: There are differing opinions on its validity or invalidity, or the condition of obtaining permission.