BibTeX:
@incollection{WrittenonbehalfofShoghiEffendi1982,
  author = {Written on behalf of Shoghi Effendi},
  title = {A Treasure of the Kingdom},
  booktitle = {Bahíyyih Khánum: The Greatest Holy Leaf},
  year = {1982},
  publisher = {Bahá'í World Centre},
  url = {https://www.gutenberg.org/ebooks/19242},
}

APA:
Written on behalf of Shoghi Effendi. (1982). A Treasure of the Kingdom. In *Bahíyyih Khánum: The Greatest Holy Leaf*. Bahá'í World Centre.

MLA:
Written on behalf of Shoghi Effendi. "A Treasure of the Kingdom." *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.

Chicago:
Written on behalf of Shoghi Effendi. "A Treasure of the Kingdom." In *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.