How do I cite the Rule of St. Benedict?
Answer
If you are using this for a class paper (which I assume is a safe assumption) then your are doing formal writing & you must follow the dictates of the style guide you professor wishes you to use, APA, MLA, etc.
So while the reference "RB 19: 1-2" makes perfect sense in what you are currently reading, it can't be used in your paper (unless your professor says that is the preferred style).
I thought the closest example to citing a book with chapter & verse would be the Bible, so I checked the Publication Manual of the American Psychological Association, 6th edition but could find no reference as to how to cite the Bible (99% of my citation questions are about APA so I am again making an assumption that you wish to cite the Rule in APA).
I spoke with another Librarian and we agree that you should treat this as a direct quote, so create a citation for the edition you have in hand of the Rule, and follow the APA rules for parenthetical references.
You could maybe add some context with your writing. The date of the edition in the parentheses will look odd.
Writing in the 5th century, Benedict stated "live in community" (1982, p. 47).
You might check with your professor, also. If she/he is assigning the Rule as a reading, you would think she/he would have seen the Rule quoted before.
Good luck with your paper.l