There is, however, in the bible, I have KJV, it says "Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?" 2 Corinthians 6:14 and 15 KJV. Many religions have that rule as well. Amish and Mennonites, JW, LDS.. even other than Christians: Islam/Muslims, etc. Even Jewish! Jewish mothers fix up their children to marry other Jewish people.
Many religion organizations' own religious books such as Korans, Torah, etc.. they DO say to be separated from others. Even for marriage. Of course, usually happens with the Fundamentalists in each religions or faith. Liberal believers will reject that notation or verse in their bibles or books and have interfaith marriages.
It is very common that marriages fail due to differences such as say as in an example, a Christian and an Atheist. Why? Those two faiths clash between the two since one of the two believes in God and the other do not believe in God at all. Most religions will say not to marry someone outside of their faiths because they KNOW the difficulties.
I am Born Again Christian and my wife is a Christian with a little differences. I may disagree with her but on other issues about our faiths agree. For example, we agree that there are many churches act like franchises and they are not with God (liberals). We believe a church in the bible means a group of believers together to fellowship, not a building, not a business, not a franchise. We read the bible together and not attending a church building.
One thing interesting to note. I wanted a true Fundamentalist--strong Christian woman but agree with my beliefs. I tried to find one in churches and failed for more than a dozen years or so (born again March 28, 1988). I found my wife at a singles dance (I know you all read it before. Ha.) because it was a bit easier to find one who isnt too focus on God. I hated this line like if you were trying to find a job. I hear this from Christian women too much, "Wait on the Lord." It really means, "Sorry Mark, I am not interested, now leave me alone!"
So, it is best interest for everyone to find someone really agree upon issues very closely. Not by the name of church. Ie-Baptists believe in marrying Baptists only. They forgot there are other Christians such as Narazeth, AnaBaptists, Assembly of God.. I know each denominations have slightly different doctrines. That is my point.