BibTeX:
@incollection{Various,
  author = {Various},
  title = {‘Abdu’l-Baha - the Knight of Light},
  booktitle = {Baha'i Stories for Children},
  url = {https://bahaistoriesforchildren.blogspot.com/2017/06/abdul-baha-knight-of-light.html},
}

APA:
Various. ‘Abdu’l-Baha - the Knight of Light. In *Baha'i Stories for Children*.

MLA:
Various. "‘Abdu’l-Baha - the Knight of Light." *Baha'i Stories for Children*, n.d..

Chicago:
Various. "‘Abdu’l-Baha - the Knight of Light." In *Baha'i Stories for Children*, n.d..