As a principle, it is permissible for a Muslim to engage, as an employee of a non-Muslim in various vital activities of life and in different kinds of [company], of general benefit so that he may be of use to himself and humanity. This permission is conditional to the fact that such work is not forbidden by the laws of Islam and that it does not lead to harming the interest of Muslims or serve the interest and schemes of the enemies of Islam and Muslims.
It is not permissible for a Muslim to debase himself in front of any human being be they Muslim or non-Muslim. So, if the work, that a Muslim does, debases him in from of a non-Muslim, it is not permissible for him to engage in that debasing work.
A Muslim is allowed to serve meat of an animal that was not slaughtered according to Islamic laws to those who consider it lawful like Christians, Jews, and others. Similarly, it is permissible for him to work in preparing and cooking that meat. The money that he receives in return for that work can be legitimized by the rule of tanãzul (withdrawing your exclusive right from that meat).
It is not permissible for a Muslim to sell pork to those who believe it is lawful for them among the Christians and others. Based on obligatory precaution, one should not even serve that meat to them. (See the question-answer section below.) A Muslim is not allowed to serve intoxicating drinks to anyone at all, even to those who believe it is lawful to them. He is not [even] allowed to wash the dishes or give them to others, if that washing and giving is part of the drinking of intoxicants.
A Muslim is not allowed to hire himself out for selling or serving intoxicanting drinks or for washing the dishes for that purpose, just as it is not allowed for him to take the wages for this work, as it is unlawful. As for the “extreme need” justification used by some people for this kind of work, it is an unacceptable justification. Almighty Allãh says, “And whosoever is careful of (his duty towards) Allãh, He will make for him an outlet; and give him in sustenance from whence he thinks not. And whosoever trusts in Allãh, He is sufficient for him…” (65:3) He also said, “Surely those whom the angels cause to die while they are unjust to their souls, they shall say, ‘In what state were you?’ They shall answer, ‘We were weak in the earth.’ They shall say, ‘Was not Allãh’s earth spacious so that you should have migrated therein?’ So, these it is whose abode is hell, and it is an evil resort except the weak from among the men and the children who have not in their power the means nor can they find a way (to escape).” (4:97-98)
In his sermon of the last pilgrimage, Prophet Muhammad (s.a.w.) said, “Know that the Trustworthy Soul (Jibra’il) has inspired in my mind that no soul shall die until its sustenance is completed. Therefore, fear Allãh and work hard in seeking [the sustenance]; and let not the delay in getting your share of the sustenance compel you to seek it through disobeying Allãh for the Blessed and Almighty Allãh has divided the sustenance among His creation by lawful means and not through unlawful means. So, whosoever fears Allãh and has patience, Allãh will provide them sustenance from lawful [means]; but whosoever tears apart the curtain of propriety, makes haste and acquire their portion from unlawful [means], it will be taken off from their lawful sustenance and they will be held accountable for it on the Day of Resurrection.”
It is not permissible to work in places of entertainment and other similar places of debauchery if that work would cause one to drift towards unlawful acts. (See the question-answer section below.) It is permissible for Muslims to participate as partners with non-Muslims (like Christians and Jews for example) in various kinds of businesses considered lawful in Islamic laws like selling, buying, export, import, building contracts, etc. It is permissible to deposit [money] in non-Muslim (private or state-owned) banks. If a Muslim intends to get a loan from such banks, it is necessary that he should do so with the intention that it is a transaction without return, even if he knows that he will end up paying the capital as well as the interest. And he should not do so with the intention of getting the loan with the condition of [paying] interest.
It is permissible for a Muslim to authorise another person to use his name (and his credit) to buy shares, in return for an amount (in money or commodity) on which both have reached an agreement. It is not permissible for a Muslim to buy products of the countries that are in a state of war with Islam and Muslims, for example, Israel.
A Muslim is allowed to exchange the currency with some other currency at the market price, or at a lower or higher rate, irrespective of the fact that the exchange is of an immediate or a deferred nature. It is forbidden to use bank-notes that are counterfeit or have no value at all—the money that is used by a fraudester when he pays the worker who is unaware of its forgery or worthlessness. The business deal conducted with this kind of money is not valid. It is not permissible for a Muslim to buy tickets of chance (including lottery), if he buys them with the intention of luckily winning the prize.
It is permissible for him to buy the lottery tickets if he buys it with the intention of participating in a charitable cause that is accepted Islamically like building hospitals, orphanages, etc., but not with the intention of winning the prize. However, this hypothetical situation is extremely difficulty to occur in non-Muslim countries that consider certain activities that are forbidden in Islam to be of a charitable nature according to their own understanding.In both the cases [of “a” and “b” if a Muslim wins the lottery], it is permissible to receive the prize from a non-Muslim [person or company].
It is permissible to sell wild animals whose meat is forbidden like tiger, hyena, fox, elephant, lion, bear, and other similar animals like cat and whale if there is any legitimate benefit which makes them valuable in the market (even if in view of only some experts of that field). Non-hunting dogs and pigs are exempt from this rule. It is permissible to sell and buy gold and silver utensils for the purpose of decoration; however, it is forbidden to use them for eating and drinking. No khums is levied on the salary paid by a government in a Muslim country directly into the bank account of its employee, even if it is more than his annual expenses—as long as he does not receive it in his hands.
Source: Ayatollah Sistani