BibTeX:
@incollection{AbdulBah1912,
  author = {'Abdu'l-Bahá},
  title = {THIRD PRINCIPLE},
  booktitle = {Paris Talks},
  year = {1912},
  publisher = {Bahá'í Publishing Trust},
  url = {https://www.gutenberg.org/cache/epub/19284/pg19284-images.html},
}

APA:
'Abdu'l-Bahá. (1912). THIRD PRINCIPLE. In *Paris Talks*. Bahá'í Publishing Trust.

MLA:
'Abdu'l-Bahá. "THIRD PRINCIPLE." *Paris Talks*, Bahá'í Publishing Trust, 1912.

Chicago:
'Abdu'l-Bahá. "THIRD PRINCIPLE." In *Paris Talks*, Bahá'í Publishing Trust, 1912.