?íyá'u'lláh (???? ????, alternate spelling: Zíyá'u'lláh) (15 August 1864 - 30 October 1898) was one of the sons of Bahá'u'lláh.
He was the second son of his father's second wife Fatimih (also known as Mahd-i-'Ulya).
He was born in Edirne (modern day Adrianople).Bahá'u'lláh gave the title Ghusn-i-Athar (meaning "Most Pure Branch" or "Purer Branch") to his son Mírzá Mihdí.
After Mírzá Mihdí's death in 1870, Bahá'u'lláh gave the same title to his other son ?íyá'u'lláh, but this is not confirmed by Bahá'í sources.He swayed between his two brothers, ?Abdu'l-Bahá and Muhammad ?Alí, in their argument.
He married Thurayyá Samandarí, daughter of Shaykh Kázim-i-Samandar and sister of Taráz'u'lláh Samandarí, a Hand of the Cause of God.
The marriage was childless.
?íyá'u'lláh died on 30 October 1898 in Haifa Palestine, and was posthumously labeled a Covenant-breaker.After his death in 1898, ?íyá'u'lláh was initially buried next to his father at the Shrine of Bahá'u'lláh at the Mansion of Bahjí.
However, having been declared a Covenant-breaker, ?íyá'u'lláh's remains were disinterred in 1965 in a process the Universal House of Justice described as a "purification...