BibTeX:
@incollection{AbdulBah1912,
  author = {'Abdu'l-Bahá},
  title = {London},
  booktitle = {'Abdu'l-Bahá in London},
  year = {1912},
  url = {https://www.gutenberg.org/cache/epub/19250/pg19250-images.html},
}

APA:
'Abdu'l-Bahá. (1912). London. In *'Abdu'l-Bahá in London*.

MLA:
'Abdu'l-Bahá. "London." *'Abdu'l-Bahá in London*, 1912.

Chicago:
'Abdu'l-Bahá. "London." In *'Abdu'l-Bahá in London*, 1912.