This seems to be a mountain folk hymn; the oldest recording I’ve come across was in The Original Folkways Recordings of Doc Watson and Clarence Ashley. These days it is usually done in a bluegrass arrangement, although everyone seems to change it just a little bit.

The book of Daniel is in the Old Testament of the Bible. In the time of the story, Israel has been conquered, and its people exiled to Babylon. In the book, the king forbids worship of any deity other than himself, but Daniel is caught praying to the Hebrew God (specifically, he prays three times a day). As a form of execution, he is thrown into a den of hungry lions. However, God sends an angel to “shut the mouths of the lions” and Daniel survives and is released.