Is it permitted to work for a facilities management company that manages a building owned by a bank?

As a principle, permissibility or impermissibility of employment in any given organisation is generally determined by: (i) The nature of the job must be lawful (halal), i.e., the work must not entail anything prohibited in the Shariah; and (ii) The salary or income one receives must come from a halal source i.e., the salary should not come from stolen or interest money. Thus we see the Messenger (saw) cursed the one who accepted usury, the one who paid it, the witness to it and the one who recorded it. (Abu Dawud: Book 22, Number 3327) Most banks however generate income in a number of different ways, some halal, some haram, thereby mixing their income, e.g., charging interest on loans, charging fees for accounts and card services, holding deposits from savers and so on. When funds become mixed in this manner, it is better to distance oneself from them, however there is no sin in receiving income from them. Furthermore as facilities management of buildings being permitted, it is permissible to accept this money as income. The Prophet (saw) said: “Leave that which is doubtful and adopt that which is not doubtful.”(Nisa'i and Tirmidhi) “What is lawful is clear and what is forbidden is clear and in between them there are some things that are doubtful, which most people do not know if they are lawful or forbidden. Whoever avoids what is doubtful, safeguards his deen and honor, but one who engages in what is doubtful, falls in what is forbidden. The example of this is like the shepherd who grazes his herd in the vicinity of an exclusively reserved pasture but it is always apprehensive some of his animals might get into the pasture. Every king has a reserved pasture and the reserved pasture of Allah is what He has forbidden.” (Sahih al-Bukhari and Muslim) The famous Hanbali jurist Ibn Qudamah (ra) noted: “If a person buys from another person whose wealth is a mixture of what is lawful and what is forbidden, like an unjust ruler and a person who deals in Riba, then one's dealing is lawful if one is sure that he deals with the lawful portion of wealth of the other person, and vice versa. But, if one does not know that, then we dislike such dealing for it is possible to be forbidden, and such dealing is valid since it also might be lawful and this is the doubtful thing. Then, the more forbidden is the other person's wealth, the more it will be forbidden to deal with him, and vice versa.” (al-Mughni) The best course of conduct is abstention from such scenarios as mentioned by Allah (swt) when he says: “And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out. And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allah, then He will suffice him. Verily, Allah will accomplish his purpose. Indeed Allah has set a measure for all things” (Qur'an al-Talaq 65:2-3)