Who said homosexuality is a sin?

The Bible never says that "being gay" is a sin, in the sense of simply being attracted to the same sex; however, Leviticus 18:22 and 20:13 both say that sex between two men is a "toeva" (usually mistranslated as "abomination," with the general meaning "something gravely forbidden"). However this verse can be interpreted a number of different ways, and there are many Christian and Jewish denominations that view it as a prohibition against same-sex rape, and not a prohibition of an expression of love.

In the New Testament Corinthians 1 6:9-10 lists homosexuals among other kinds of sexual sinners, and Paul describes God "giving [men and women] up to passions of dishonor" by allowing them to undergo homosexual acts (Romans 1:26-27) [all of which are mistranslations of the Greek text].