BibTeX:
@incollection{Bahullh1858,
  author = {Bahá'u'lláh},
  title = {Hidden Word, Arabic 5: My Mansion is the Heart},
  booktitle = {The Hidden Words},
  year = {1858},
  publisher = {Bahá'í Publishing Trust},
  url = {https://www.bahai.org/library/authoritative-texts/bahaullah/hidden-words/},
}

APA:
Bahá'u'lláh. (1858). Hidden Word, Arabic 5: My Mansion is the Heart. In *The Hidden Words*. Bahá'í Publishing Trust.

MLA:
Bahá'u'lláh. "Hidden Word, Arabic 5: My Mansion is the Heart." *The Hidden Words*, Bahá'í Publishing Trust, 1858.

Chicago:
Bahá'u'lláh. "Hidden Word, Arabic 5: My Mansion is the Heart." In *The Hidden Words*, Bahá'í Publishing Trust, 1858.