The primary source of Biblical authority for the condemnation of homosexuality is in the Old Testament's Book of Leviticus 18:22.
"You shall not lie with a man as with a woman; it is abomination."
The next verse prescribes death as the punishment for violation of the Law.
This is the single unambiguous condemnation of homosexuality in the Bible. Other claimed references are inferential or derivative, at best. But there is no lack of controversy about the interpretation and context of Leviticus 18:22. The most important issue is that Leviticus is the book that deals with ritual hygiene of the ancient Jewish priesthood.
The key word in Leviticus 18:22 is abomination, which is translated from the Hebrew toeyvah. What is interesting is that toeyvah also means "ritually impure" or "sinful". Thus, there may not necessarily be a moral judgement implied by toeyvah, only that being toeyvah makes one unfit for Jewish rituals.