BibTeX:
@incollection{BahyyihKhnumandothers1982,
  author = {Bahíyyih Khánum and others},
  title = {15: The Guardian of the Cause of God has},
  booktitle = {Bahíyyih Khánum},
  year = {1982},
  url = {https://www.gutenberg.org/cache/epub/19242/pg19242-images.html},
}

APA:
Bahíyyih Khánum and others. (1982). 15: The Guardian of the Cause of God has. In *Bahíyyih Khánum*.

MLA:
Bahíyyih Khánum and others. "15: The Guardian of the Cause of God has." *Bahíyyih Khánum*, 1982.

Chicago:
Bahíyyih Khánum and others. "15: The Guardian of the Cause of God has." In *Bahíyyih Khánum*, 1982.