He works in marketing of a program to deal in shares

Question

Praise be to Allah.

The basic principle with regard to such products that may be
used for both halaal or haraam purposes is that reference should be make to
knowledge and certainty about the purchaser or user.

If it is certain that they are going to be used for haraam
purposes, then it is not permissible to produce them or sell them.

If it is certain that they are going to be used for
permissible purposes, then there is no dispute that it is permissible to
produce them and sell them.

If both are possible, and we do not know whether people will
use them for halaal or haraam purposes, then we should act on the basis of
what we think is most likely. If the producer or seller thinks it most
likely that the buyer will use it for haraam purposes, then it is haraam to
sell it to him. If he thinks it most likely that he will use it for halaal
purposes then it is halaal to sell it to him.

Unfortunately if we study the stock market in the Arab and
Muslim world – let alone the West – we will see that most of the shares that
are bought and sold in those markets are shares in haraam companies such as
banks, insurance companies and companies that make haraam products, and
those that buy and sell permissible products take riba-based loans and
invest their wealth in riba-based banks. These are what some contemporary
scholars call “mixed companies” and companies whose shares are haraam
according to the correct opinion.

Hence it is not permissible for anyone to help these stock
markets with their work, because of the definitively haraam things that it
involves, or because of the haraam that is mixed with halaal, and the halaal
is very small in comparison with the haraam. Based on this, we do not think
that you should work in marketing these programs, because it is cooperating
in sin and transgression, and Allaah says (interpretation of the meaning):

“do not help one another in sin and transgression. And
fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him)
said:

Every garment that it is thought most likely will be used for
sinful purposes, it is not permissible to sell or tailor it for one who is
going to use it for sinful and wrong purposes. End quote.

Sharh al-‘Umdah (4/386).

In the answer to question no.
11517 we quoted the response
of Shaykh Ibn al-‘Uthaymeen (may Allaah have mercy on him) (to a question)
about the ruling on operating a computer program for a company that would
use it for both halaal and haraam purposes. The Shaykh replied:

If most of the work which this company does is haraam, then
it is not permissible for him to do that. If most of what they do is
permitted, then it is permissible for him to do it. If they (haraam and
halaal elements) are the same, then he should not do it, on the assumption
that what is haraam will outweigh what is halaal. And Allaah knows best.

For more information, please see the answer to question no.
75007.

And Allaah knows best.