BibTeX:
@incollection{AbdulBah1908,
  author = {'Abdu'l-Bahá},
  title = {20: THE NECESSITY OF BAPTISM},
  booktitle = {Some Answered Questions},
  year = {1908},
  url = {https://www.gutenberg.org/cache/epub/19289/pg19289-images.html},
}

APA:
'Abdu'l-Bahá. (1908). 20: THE NECESSITY OF BAPTISM. In *Some Answered Questions*.

MLA:
'Abdu'l-Bahá. "20: THE NECESSITY OF BAPTISM." *Some Answered Questions*, 1908.

Chicago:
'Abdu'l-Bahá. "20: THE NECESSITY OF BAPTISM." In *Some Answered Questions*, 1908.