BibTeX:
@incollection{Various,
  author = {Various},
  title = {Mírzá Músá: Bahá’u’lláh’s faithful brother, also known as Áqáy-i-Kalím – a brief account of his life by 'Abdu'l-Baha},
  booktitle = {Baha'i Stories Blog},
  url = {https://bahaistories.blogspot.com/2018/12/mirza-musa-bahaullahs-faithful-brother.html},
}

APA:
Various. Mírzá Músá: Bahá’u’lláh’s faithful brother, also known as Áqáy-i-Kalím – a brief account of his life by 'Abdu'l-Baha. In *Baha'i Stories Blog*.

MLA:
Various. "Mírzá Músá: Bahá’u’lláh’s faithful brother, also known as Áqáy-i-Kalím – a brief account of his life by 'Abdu'l-Baha." *Baha'i Stories Blog*, n.d..

Chicago:
Various. "Mírzá Músá: Bahá’u’lláh’s faithful brother, also known as Áqáy-i-Kalím – a brief account of his life by 'Abdu'l-Baha." In *Baha'i Stories Blog*, n.d..