What is the reason for mental illness despite maintaining remembrance (adhkar) and supplications (du'as), and what are the acts of worship (ibadat) in which deputization (tawkeel) is permissible and those in which it is not?

There are two matters: First, what is presumed to be a spiritual illness might be an illusion, and the person should consult psychiatrists, in compliance with the Prophet's (peace be upon him) recommendation to seek medical treatment. Second, there are acts of worship in which agency (delegation) is permissible, such as giving charity and zakat, and sacrificing an udhiyah, and this includes appointing someone to perform Hajj on behalf of an incapacitated person. And there are acts of worship in which agency is not permissible, such as prayer, fasting, and reading the Quran. Ibn Uthaymeen explained that the rights of Allah are divided into three categories: financial acts of worship in which agency is absolutely permissible; physical acts of worship in which delegation is absolutely impermissible; and a category in which delegation is permissible with details, such as Hajj for one who is unable. The general rule is that agency is not permissible in the rights of Allah, because they aim to establish worship of Allah from the person himself.