Can money donated to the masjid by non Muslims be used for maintenance of the masjid?
In the Name of Allah, the Most Gracious, the Most Merciful.
Donations for the maintenance of a masjid or an Islamic center can be accepted from a non-Muslim individual or organization with the condition that such donations are not, in any manner, harmful to the interests of the Muslims. If, for example, there is an apprehension that the donors will try to interfere with the management of the Masjid or the donation will be detrimental to the esteem of the Muslims, then, such donations should not be accepted.
So far as the question of the source of income of the donor is concerned, it is not necessary to carry out a detailed enquiry in this respect. However, if the source of income on the face of it, is proved to be haram, the donation should not be accepted.
Donating monies for the upliftment and maintenance of Masaajid, the houses of Allah Ta’ala, is a very honorable and blessed cause, and the Muslim community should endeavor to fill such opportunities.
And Allah Ta’āla Knows Best.
Mufti Arshad Ali
Darul Iftaa, Jaamia Madinatul Uloom (Trinidad)
 Contemporary Fatawaa (Mufti Muhammad Taqi Usmani) pg.333