BibTeX:
@incollection{BahyyihKhnumandothers1982,
  author = {Bahíyyih Khánum and others},
  title = {21: The passing away of the Greatest Holy Leaf},
  booktitle = {Bahíyyih Khánum},
  year = {1982},
  url = {https://www.gutenberg.org/cache/epub/19242/pg19242-images.html},
}

APA:
Bahíyyih Khánum and others. (1982). 21: The passing away of the Greatest Holy Leaf. In *Bahíyyih Khánum*.

MLA:
Bahíyyih Khánum and others. "21: The passing away of the Greatest Holy Leaf." *Bahíyyih Khánum*, 1982.

Chicago:
Bahíyyih Khánum and others. "21: The passing away of the Greatest Holy Leaf." In *Bahíyyih Khánum*, 1982.