BibTeX:
@incollection{RyyihRabbnRyyihKhnum1969,
  author = {Rúḥíyyih Rabbání (Rúḥíyyih Khánum)},
  title = {The Guardian's Gardens at Bahjí},
  booktitle = {The Priceless Pearl},
  year = {1969},
  publisher = {George Ronald},
}

APA:
Rúḥíyyih Rabbání (Rúḥíyyih Khánum). (1969). The Guardian's Gardens at Bahjí. In *The Priceless Pearl*. George Ronald.

MLA:
Rúḥíyyih Rabbání (Rúḥíyyih Khánum). "The Guardian's Gardens at Bahjí." *The Priceless Pearl*, George Ronald, 1969.

Chicago:
Rúḥíyyih Rabbání (Rúḥíyyih Khánum). "The Guardian's Gardens at Bahjí." In *The Priceless Pearl*, George Ronald, 1969.