His mother wants him to study medicine and he wants to enter the business field
The mother’s rights over her son are great; he is required to honour her and treat her kindly as enjoined by Allah in many places in His Book and as enjoined by His Messenger (blessings and peace of Allah be upon him).
Hence you should try to convince her of the advantages of the field to which you are inclined and want to enter and in which you feel that you are able to succeed.
This is something that some fathers and mothers neglect. They look at the beauties of the specialty or profession but they do not look at how suited the son is for it or his desire to succeed in it. The son may have no desire to study medicine for example, or he may feel that he has no need for it or it is not possible for him to excel in it. Yet despite that his parents insist that he should study medicine. This destroys real talents and contributes to increasing the numbers of graduates who are not fully qualified in their specialty.
The son is not obliged to obey his parents in choosing a specialty to study or a field of work, just as he is not obliged to eat what he does not like or marry someone who he does not want.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: The parents have no right to force their son to marry someone who he does not want, and he is not disobeying them in that case; the same applies to eating food he does not want.
End quote from al-Ikhtiyaaraat, p. 304
As he is not obliged to obey them in eating what he does not want, even though the hardship involved does not last more than a brief period of time, it is more appropriate that he should not be obliged to obey them with regard to study which will take years and on which years of further work will be based, when he has no interest in doing that.
What you have to do is strive hard to please your mother and make her feel good, and prove that you can excel and succeed in the field of business and commerce.
We ask Allah to guide and help you.
And Allah knows best.