BibTeX:
@incollection{AbdulBah1943,
  author = {'Abdu'l-Bahá},
  title = {SPIRITUAL KNOWLEDGE},
  booktitle = {Bahá'í World Faith},
  year = {1943},
  url = {https://www.gutenberg.org/cache/epub/19239/pg19239-images.html},
}

APA:
'Abdu'l-Bahá. (1943). SPIRITUAL KNOWLEDGE. In *Bahá'í World Faith*.

MLA:
'Abdu'l-Bahá. "SPIRITUAL KNOWLEDGE." *Bahá'í World Faith*, 1943.

Chicago:
'Abdu'l-Bahá. "SPIRITUAL KNOWLEDGE." In *Bahá'í World Faith*, 1943.