Ruling on Muslim praying in the house of a Christian

It is permissible to pray
in the house of a Christian or anyone else who does not follow the religion
of Islam because of the general meaning of the words of the Prophet
(blessings and peace of Allah be upon him): “… the earth has been made for
me a place of prostration and a means of purification, so wherever a man of
my ummah is when the time for prayer comes, let him pray…”

Narrated by al-Bukhaari,
323 

As-Sindi (may Allah have
mercy on him) said: What we learn from the hadeeth is that the earth itself
in its entirety is a place for prayer, unless there is any impediment in the
presence of which prayer is makrooh or invalid, in which case the ruling is
connected to that impediment.

End quote from Haashiyat
as-Sindi, commentary on Saheeh al-Bukhaari, 1/140 

Al-Bukhaari gave a chapter
in his Saheeh the title “Chapter on prayer in churches”, in which he
narrated that ‘Umar (may Allah be pleased with him) said: We do not enter
churches because of the statues on which there are images. And Ibn ‘Abbaas
used to pray in churches except a church in which there were statues. 

Al-Haafiz ibn Hajar (may
Allah have mercy on him) said: With regard to the fact that he said “Chapter
on praying in churches”, the author of al-Muhkam said: The ruling on
churches applies to churches, synagogues, monks’ cells, temples in which
there are idols, fire temples and so on.

End quote from Fath
al-Baari, 1/531. See also al-Insaaf by al-Mirdaawi, 1/496 

If prayers offered in
churches are valid, then it is more appropriate that they should be valid if
offered in the house of a Christian or other non-Muslim. 

The scholars of the
Standing Committee (6/270) were asked: Sometimes the time for prayer comes
when I am in the house of a Christian, so I take my prayer mat and pray in
front of them. Is my prayer is valid, because I am in one of their houses? 

They replied: 

Yes, your prayer is valid;
may Allah increase you in keenness to obey Him, especially by offering the
five daily prayers on time. It is obligatory to try to offer them in
congregation, frequenting the mosques as much as possible. End quote. 

Standing Committee for
Academic Research and Issuing Fatwas. 

And Allah knows best.