BibTeX:
@incollection{Bahullh1982,
  author = {Bahá'u'lláh},
  title = {Let These Exalted Words Be Thy Love-Song},
  booktitle = {Bahíyyih Khánum},
  year = {1982},
  url = {https://www.gutenberg.org/cache/epub/19242/pg19242-images.html},
}

APA:
Bahá'u'lláh. (1982). Let These Exalted Words Be Thy Love-Song. In *Bahíyyih Khánum*.

MLA:
Bahá'u'lláh. "Let These Exalted Words Be Thy Love-Song." *Bahíyyih Khánum*, 1982.

Chicago:
Bahá'u'lláh. "Let These Exalted Words Be Thy Love-Song." In *Bahíyyih Khánum*, 1982.