BibTeX:
@incollection{Bahullh1873,
  author = {Bahá'u'lláh},
  title = {The King of Festivals: Bahá'u'lláh's Own Naming of Riḍván},
  booktitle = {The Kitáb-i-Aqdas},
  year = {1873},
  publisher = {Bahá'í Publishing Trust},
  url = {https://www.bahai.org/library/authoritative-texts/bahaullah/kitab-i-aqdas/},
}

APA:
Bahá'u'lláh. (1873). The King of Festivals: Bahá'u'lláh's Own Naming of Riḍván. In *The Kitáb-i-Aqdas*. Bahá'í Publishing Trust.

MLA:
Bahá'u'lláh. "The King of Festivals: Bahá'u'lláh's Own Naming of Riḍván." *The Kitáb-i-Aqdas*, Bahá'í Publishing Trust, 1873.

Chicago:
Bahá'u'lláh. "The King of Festivals: Bahá'u'lláh's Own Naming of Riḍván." In *The Kitáb-i-Aqdas*, Bahá'í Publishing Trust, 1873.