Responding to this issue, we would like to cite the fatwa of, Dr. Monzer Kahf, a prominent economist and counselor, who stated:
“…it is permissible to receive donations that you do not know their sources to build mosques and other Islamic social and educational services, etc. You need not to ask about sources and you need not to know.
However, if you know for full surety that the exact money given as a donation it itself came from interest and the like just do not use it for the part of the mosque that is the prayer hall. You can use it for other sections of the building and for other projects like education and social services. This is not a sharia requirement in the full sense it is only to keep the prayer hall pure of any such Haram. Of course if you do not know the exact source of the money you assume that it is permissible because people, Muslims and non-Muslims alike are decent unless proven otherwise. This means that you can accept donations from Muslims and from non-Muslims for the mosque and other projects.
Additionally, If you know that a given cash came to the hand of the donor by shameful (immoral), illegal means such as theft YOU MUST NOT ACCEPT SUCH CASH AS A DONATION OR EVEN AS A SALE PRICE OF A SPECIFIC GOOD AND SERVICE. Of course this rule only applies to the specific cash not to presumed or even known source. For instance we may assume that the source of income of a prostitute is all Haram or we may know it is YET WE ARE NOT ASKED IN SHARI’AH TO BOYCOTT HER, NOT SELL HER FOOD, CLOTH OR SHELTER UNTIL SHE STARVED TO DEATH. This kind of harsh and inhumane behavior does not exist in our religion.”