BibTeX:
@incollection{LouisGGregory1911,
  author = {Louis G. Gregory},
  title = {Louis Gregory at the Tomb of the Báb},
  booktitle = {A Heavenly Vista: The Pilgrimage of Louis G. Gregory},
  year = {1911},
  url = {https://bahai-library.com/gregory_heavenly_vista},
}

APA:
Louis G. Gregory. (1911). Louis Gregory at the Tomb of the Báb. In *A Heavenly Vista: The Pilgrimage of Louis G. Gregory*.

MLA:
Louis G. Gregory. "Louis Gregory at the Tomb of the Báb." *A Heavenly Vista: The Pilgrimage of Louis G. Gregory*, 1911.

Chicago:
Louis G. Gregory. "Louis Gregory at the Tomb of the Báb." In *A Heavenly Vista: The Pilgrimage of Louis G. Gregory*, 1911.