BibTeX:
@incollection{Various,
  author = {Various},
  title = {In Edinburgh, ‘Abdu’l-Bahá addressed the Esperantists},
  booktitle = {bahaistories.com archive},
  url = {https://bahaistories.com/subject/universal-language},
}

APA:
Various. In Edinburgh, ‘Abdu’l-Bahá addressed the Esperantists. In *bahaistories.com archive*.

MLA:
Various. "In Edinburgh, ‘Abdu’l-Bahá addressed the Esperantists." *bahaistories.com archive*, n.d..

Chicago:
Various. "In Edinburgh, ‘Abdu’l-Bahá addressed the Esperantists." In *bahaistories.com archive*, n.d..