BibTeX:
@incollection{AbdulBah1886,
  author = {'Abdu'l-Bahá},
  title = {'Abdu'l-Bahá's Account of the Martyrdom},
  booktitle = {A Traveler's Narrative},
  year = {1886},
  publisher = {Cambridge University Press},
  url = {https://www.bahai.org/library/authoritative-texts/abdul-baha/travelers-narrative/},
}

APA:
'Abdu'l-Bahá. (1886). 'Abdu'l-Bahá's Account of the Martyrdom. In *A Traveler's Narrative*. Cambridge University Press.

MLA:
'Abdu'l-Bahá. "'Abdu'l-Bahá's Account of the Martyrdom." *A Traveler's Narrative*, Cambridge University Press, 1886.

Chicago:
'Abdu'l-Bahá. "'Abdu'l-Bahá's Account of the Martyrdom." In *A Traveler's Narrative*, Cambridge University Press, 1886.