BibTeX:
@incollection{AbdulBah1886,
  author = {'Abdu'l-Bahá},
  title = {Why Persecution Spread the Faith},
  booktitle = {A Traveler's Narrative Written to Illustrate the Episode of the Báb},
  year = {1886},
  publisher = {Cambridge University Press},
  url = {https://www.gutenberg.org/ebooks/19300},
}

APA:
'Abdu'l-Bahá. (1886). Why Persecution Spread the Faith. In *A Traveler's Narrative Written to Illustrate the Episode of the Báb*. Cambridge University Press.

MLA:
'Abdu'l-Bahá. "Why Persecution Spread the Faith." *A Traveler's Narrative Written to Illustrate the Episode of the Báb*, Cambridge University Press, 1886.

Chicago:
'Abdu'l-Bahá. "Why Persecution Spread the Faith." In *A Traveler's Narrative Written to Illustrate the Episode of the Báb*, Cambridge University Press, 1886.