Knowledge is of two kinds: one of which is compulsory and the other optional.

Concerning the compulsory type of knowledge, the Prophet (s) said: "Seeking knowledge is incumbent upon every Muslims", related by Tabarani from Ibn Abbas. This is no doubt an obligation upon every person believing in Allah as the one and only true Lord and Muhammad as His prophet (s). This knowledge includes: belief in Allah, the Angels, the Holy books (revelations), the prophets, the last day and fate. He must also understand the evils of associating gods with Allah, hypocrisy and disbelief. Then he must learn what is lawful and prohibited, in order that when he comes to pray he will know how to perform his prayers according to the Prophet's (s) way. If he lives till the holy month of Ramadan, he should learn all about fasting and the rules applying to it, including the good practises of the Holy Prophet (s), and so on.

As for optional knowledge, it becomes optional only when it is undertaken by some people. This knowledge includes the essential studies for this world, such as medicine, maths, science and so forth. Also the study of "Shariah" - Islamic studies like the science of Muslim creed and its branches, and the names of the men of ahadith and others.