When is it permissible for a student of knowledge to take from zakat, and does this apply to the affluent person who dedicates himself to teaching without charge, or to the preacher who dedicates himself, and is it permissible to spend on the service of da‘wah from zakat?

It is permissible for a da'i (caller to Islam) and a full-time, poor student of knowledge to receive zakat. However, if he has enough to suffice him or is able to earn a living, then it is not permissible for him to do so. It was also said that it is permissible to receive zakat even if he is able to earn a living, provided he dedicates himself to seeking knowledge, as if his pursuit of knowledge permits him to ask for zakat and other forms of charity. It is stated in Al-Majmu' by Al-Nawawi that zakat is permissible for one who is engaged in acquiring Islamic knowledge, even if he is able to earn a living befitting his status, if earning would hinder him from acquiring knowledge, because seeking knowledge is a collective obligation (fard kifaya). Ibn Hajar al-Haytami said that it is permissible to take zakat in the amount sufficient for one who is preoccupied from earning a lawful living by studying Islamic knowledge or the Quran. He is also allowed to spend what he receives on buying books of Islamic knowledge and its tools. What is said about the student of knowledge also applies to the da'i and the Quran memorizer.