BibTeX:
@incollection{AbdulBah1909,
  author = {'Abdu'l-Bahá},
  title = {How the Day of the Covenant Began},
  booktitle = {Tablets of 'Abdu'l-Bahá Abbas},
  year = {1909},
  publisher = {Bahai Publishing Society},
  url = {https://www.gutenberg.org/ebooks/19312},
}

APA:
'Abdu'l-Bahá. (1909). How the Day of the Covenant Began. In *Tablets of 'Abdu'l-Bahá Abbas*. Bahai Publishing Society.

MLA:
'Abdu'l-Bahá. "How the Day of the Covenant Began." *Tablets of 'Abdu'l-Bahá Abbas*, Bahai Publishing Society, 1909.

Chicago:
'Abdu'l-Bahá. "How the Day of the Covenant Began." In *Tablets of 'Abdu'l-Bahá Abbas*, Bahai Publishing Society, 1909.