BibTeX:
@incollection{BahyyihKhnumandothers1982,
  author = {Bahíyyih Khánum and others},
  title = {51: I was very glad to know of your meeting ...},
  booktitle = {Bahíyyih Khánum},
  year = {1982},
  url = {https://www.gutenberg.org/cache/epub/19242/pg19242-images.html},
}

APA:
Bahíyyih Khánum and others. (1982). 51: I was very glad to know of your meeting .... In *Bahíyyih Khánum*.

MLA:
Bahíyyih Khánum and others. "51: I was very glad to know of your meeting ...." *Bahíyyih Khánum*, 1982.

Chicago:
Bahíyyih Khánum and others. "51: I was very glad to know of your meeting ...." In *Bahíyyih Khánum*, 1982.