If the Muslim understands that the purpose and aim of his being created in this world is to adhere to the laws of Allaah, and to worship Allaah by doing so, then he will also understand that it is essential for him to learn the rulings of Allaah’s laws and learn what his duties are. That is because what is needed in order to do what is obligatory is also obligatory.  

It says in the hadeeth that the Prophet (peace and blessings of Allaah be upon him) said: “Seeking knowledge is obligatory for every Muslim.” Narrated by Ibn Maajah (224) and classed as hasan because of its many isnaads and corroborating reports by al-Mazzi, al-Zarkashi, al-Suyooti, al-Sakhaawi, al-Dhahabi, al-Manaawi, and al-Zarqaani. It is also in Saheeh Ibn Maajah by al-Albaani. 

The scholars have stated that the meaning of this hadeeth is saheeh. 

Ibn ‘Abd al-Barr (may Allaah have mercy on him) said:  

But its meaning is saheeh in their opinion, even though they differed somewhat concerning it. End quote. 

Jaami’ Bayaan al-‘Ilm (1/53). 

Al-Nawawi said something similar in al-Manthooraat (p. 287), as did Ibn al-Qayyim in Miftaah Daar al-Sa’aadah (1/480). 

Ibn ‘Abd al-Barr also said: 

The scholars are unanimously agreed that acquiring some types of knowledge is an individual obligation, which each person must learn for himself, and acquiring other types of knowledge is a communal obligation – if some people acquire it then the obligation of others is waived. End quote. 

Jaami’ Bayaan al-‘Ilm wa Fadlihi (1/56). 

The scholars (may Allaah have mercy on them) have described the knowledge which must be learned on an individual basis, and they have spoken of the amount of knowledge which each Muslim must acquire. They said that this includes learning the rulings on selling for those who engage in trade, so that they will not do anything haraam or fall into riba (usury) without realizing. There are reports from the Sahaabah (may Allaah be pleased with them) which support that. 

‘Umar ibn al-Khattaab (may Allaah be pleased with him) said: “No one should sell in our marketplace except those who have knowledge of Islam.” Narrated by al-Tirmidhi (487) who said: it is hasan ghareeb. It was also classed as hasan by al-Albaani in Saheeh al-Tirmidhi. 

‘Ali ibn Abi Taalib (may Allaah be pleased with him) said: “Whoever engages in trade before learning will fall into riba, then fall into riba.” 

Mughni al-Muhtaaj (2/22). 

Ibn ‘Abd al-Barr said: 

What all people must learn is that which they cannot afford to be ignorant of such as bearing witness verbally and believing in the heart that Allaah is One and has no partner or associate, and that His names and attributes are eternal; He has no beginning and no end, and He has risen over the Throne. 

He should bear witness that Muhammad is His slave and Messenger, and that all people will be resurrected after death to be rewarded or punished for their deeds, and that the Qur’aan is the word of Allaah, and that what is in it is true.  

He should affirm that the five daily prayers are obligatory, and he must know what is essential for the performance of the prayer, such as purification and other rulings. 

He should affirm that fasting Ramadaan is obligatory, and he must know what invalidates the fast and what is essential for the completion of the fast. 

If he has enough wealth and is physically able to perform Hajj, he must know what zakaah is due on, and when it becomes due, and on how much it is due. He must perform Hajj once in his life if he has the means.

And there are things that he must know in general and he has no excuse for not knowing: such as the fact that zina and riba are forbidden, as are alcohol, pork, eating dead meat and all impure things, embezzling, bearing false witness, consuming people’s wealth unlawfully, all kinds of wrongdoing and oppression, marrying one’s mother or sister or any of those who are mentioned with them, and killing a believer unlawfully. 

And he must know all other things that are mentioned in the Book and that the ummah is agreed upon. End quote. 

Jaami’ Bayaan al-‘Ilm (1/57). 

It says in al-Mawsoo’ah al-Fiqhiyyah (30/293): 

Ibn ‘Aabideen said, quoting from al-‘Allaami: 

It is obligatory for every accountable person, male or female , after learning about religion and guidance, to learn about wudoo’, ghusl, prayer, fasting, zakaah for those who have the nisaab (minimum threshold of wealth) and Hajj for those for whom it is obligatory. 

Merchants must also learn the rulings on trade, so that they can avoid doubtful and makrooh things in their transactions; the same applies to those who follow professions. 

Everyone who works with something must learn the rulings concerning it so that he can avoid what is haraam. 

Al-Nawawi said: As for selling, marriage and the like – which are not obligatory per se – it is haraam to engage in them until one has learned their conditions. End quote. 

Al-Ghazaali (may Allaah have mercy on him) said: 

If a Muslim is a merchant and riba is widespread in the land, he must learn about the prohibition on riba. This is knowledge which is an individual obligation, i.e., knowledge of how to do what is required. End quote. 

Ihya’ ‘Uloom al-Deen (1/33). 

‘Ali ibn al-Hasan ibn Shaqeeq said to Ibn al-Mubaarak: 

What can the believer do with knowledge except seeking it? What is he obliged to learn? 

He said: Cannot afford to do anything without knowledge, and he cannot avoid asking. 

Narrated by Ibn ‘Abd al-Barr in Jaami’ Bayaan al-‘Ilm (1/56). 

Al-Ghazaali (may Allaah have mercy on him) said: 

Every person in his daily life is bound to face new issues with regard to his worship and dealings with others. So he must ask about everything, whatever new issues he encounters, and he must hasten to find out about what he expects to face before he faces it.  

Ihya’ ‘Uloom al-Deen (1/34). 

Our advice to those who work in trade and buying and selling is to read some of the books that have been written about the fiqh of transactions, such as al-Mulakhkhas al-Fiqhi by Shaykh Saalih al-Fawzaan, and Ma la Yas’u al-Taajir Jahlulu by Prof. ‘Abd-Allaah al-Muslim and Salaah al-Saawi. 

And Allaah knows best. 

See also question no. 20092.