Daniel in the lions' den

Daniel in the lions' den refers to a story in Chapter 6 of the Book of Daniel in the Bible. Daniel – a noble Jewish youth and Biblical prophet – continues to pray to the God of Israel instead of his royal master, Darius the Mede. As a result, he is sent into a den of lions to be eaten. However, an angel sent by God saves Daniel and he emerged miraculously unharmed the next day. 
By analogy, Daniel's situation has become an English language idiom for a hostile environment.