BibTeX:
@incollection{Various1982,
  author = {Various},
  title = {A Letter from the Greatest Holy Leaf},
  booktitle = {Bahíyyih Khánum: The Greatest Holy Leaf},
  year = {1982},
  publisher = {Bahá'í World Centre},
}

APA:
Various. (1982). A Letter from the Greatest Holy Leaf. In *Bahíyyih Khánum: The Greatest Holy Leaf*. Bahá'í World Centre.

MLA:
Various. "A Letter from the Greatest Holy Leaf." *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.

Chicago:
Various. "A Letter from the Greatest Holy Leaf." In *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.