BibTeX:
@incollection{AdibTaherzadeh1974,
  author = {Adib Taherzadeh},
  title = {The Tablet to Pope Pius IX},
  booktitle = {The Revelation of Bahá'u'lláh (4 volumes)},
  year = {1974},
  publisher = {George Ronald},
}

APA:
Adib Taherzadeh. (1974). The Tablet to Pope Pius IX. In *The Revelation of Bahá'u'lláh (4 volumes)*. George Ronald.

MLA:
Adib Taherzadeh. "The Tablet to Pope Pius IX." *The Revelation of Bahá'u'lláh (4 volumes)*, George Ronald, 1974.

Chicago:
Adib Taherzadeh. "The Tablet to Pope Pius IX." In *The Revelation of Bahá'u'lláh (4 volumes)*, George Ronald, 1974.