Fathwa - Doubt concerning the Cleanliness of the Placeof Prayer

Question:
When any of us moves from one apartment to another – bearing in mind
that all of the apartments are carpeted – is it permissible for us to
pray on them, since we don't know whether the previous occupants were
Muslims or not?
Answer:
Essentially, all things are considered pure, so nothing may be ruled
as impure, unless there is some evidence to show that a particular
thing is unclean, and this proven uncleanness is present inthis place.
If these two things are not proven, then the Muslim may pray, and his
prayer will be correct.
And may peace and blessings be upon our Prophet, Muhammad and upon his
family and Companions.