The Kitáb-i-Aqdas - The Most Holy Book
Index term: by Mírzá Yahyá, under Claim to Revelation
n190.
O source of perversion!
This is a reference to Mírzá Yahyá, known as Subh-i-Azal (Morning of Eternity), a younger half-brother of Bahá'u'lláh, who arose against Him and opposed His Cause. Mírzá Yahyá was nominated by the Báb to serve as a figure-head for the Bábí community pending the imminent manifestation of the Promised One. At the instigation of Siyyid Muhammad-i-Isfahání (see note 192), Mírzá Yahyá betrayed the trust of the Báb, claimed to be His successor, and intrigued against Bahá'u'lláh, even attempting to have Him murdered. When Bahá'u'lláh formally declared His Mission to him in Adrianople, Mírzá Yahyá responded by going to the length of putting forward his own claim to be the recipient of an independent Revelation. His pretensions were eventually rejected by all but a few, who became known as Azalís (see note 177). He is described by Shoghi Effendi as the "Arch-Breaker of the Covenant of the Báb" (see God Passes By, chapter X).
n192.
God hath laid hold on him who led thee astray.
A reference to Siyyid Muhammad-i-Isfahání, who is described by Shoghi Effendi as the "Antichrist of the Bahá'í Revelation". He was a man of corrupt character and great personal ambition who induced Mírzá Yahyá to oppose Bahá'u'lláh and to claim prophethood for himself (see note 190). Although he was an adherent of Mírzá Yahyá, Siyyid Muhammad was exiled with Bahá'u'lláh to 'Akká. He continued to agitate and plot against Bahá'u'lláh. In describing the circumstances of his death, Shoghi Effendi has written in God Passes By:

A fresh danger now clearly threatened the life of Bahá'u'lláh. Though He Himself had stringently forbidden His followers, on several occasions, both verbally and in writing, any retaliatory acts against their tormentors, and had even sent back to Beirut an irresponsible Arab convert, who had meditated avenging the wrongs suffered by his beloved Leader, seven of the companions clandestinely sought out and slew three of their persecutors, among whom were Siyyid Muhammad and Áqá Ján.
The consternation that seized an already oppressed community was indescribable. Bahá'u'lláh's indignation knew no bounds. "Were We", He thus voices His emotions, in a Tablet revealed shortly after this act had been committed, "to make mention of what befell Us, the heavens would be rent asunder and the mountains would crumble." "My captivity", He wrote on another occasion, "cannot harm Me. That which can harm Me is the conduct of those who love Me, who claim to be related to Me, and yet perpetrate what causeth My heart and My pen to groan."