BibTeX:
@incollection{AbdulBah1915,
  author = {'Abdu'l-Bahá},
  title = {Guidance unto the Ignorant},
  booktitle = {Memorials of the Faithful},
  year = {1915},
}

APA:
'Abdu'l-Bahá. (1915). Guidance unto the Ignorant. In *Memorials of the Faithful*.

MLA:
'Abdu'l-Bahá. "Guidance unto the Ignorant." *Memorials of the Faithful*, 1915.

Chicago:
'Abdu'l-Bahá. "Guidance unto the Ignorant." In *Memorials of the Faithful*, 1915.