BibTeX:
@incollection{Various,
  author = {Various},
  title = {‘Abdu’l-Baha tells the story of Baha’u’llah’s agreement to perform any miracle agreed on…},
  booktitle = {Baha'i Stories Blog},
  url = {https://bahaistories.blogspot.com/2013/02/abdul-baha-tells-story-of-bahaullahs.html},
}

APA:
Various. ‘Abdu’l-Baha tells the story of Baha’u’llah’s agreement to perform any miracle agreed on…. In *Baha'i Stories Blog*.

MLA:
Various. "‘Abdu’l-Baha tells the story of Baha’u’llah’s agreement to perform any miracle agreed on…." *Baha'i Stories Blog*, n.d..

Chicago:
Various. "‘Abdu’l-Baha tells the story of Baha’u’llah’s agreement to perform any miracle agreed on…." In *Baha'i Stories Blog*, n.d..