Sahih Bukhari
Divorce
Volume: 007 / Book Number: 063 / Hadith Number: 209
Narrated Nafi':
Whenever Ibn 'Umar was asked about marrying a Christian lady or a Jewess, he would say: "Allah has made it unlawful for the believers to marry ladies who ascribe partners in worship to Allah, and I do not know of a greater thing, as regards to ascribing partners in worship, etc. to Allah, than that a lady should say that Jesus is her Lord although he is just one of Allah's slaves."