On another occasion this same Mírzá Yaḥyá had, according to the testimony of one of his wives, who had temporarily deserted him and revealed the details of the above-mentioned act, poisoned the well which provided water for the family and companions of Bahá’u’lláh, in consequence of which the exiles manifested strange symptoms of illness. He even had, gradually and with great circumspection, disclosed to one of the companions, Ustád Muḥammad-‘Alíy-i-Salmání, the barber, on whom he had lavished great marks of favor, his wish that he, on some propitious occasion, when attending Bahá’u’lláh in His bath, should assassinate Him. “So enraged was Ustád Muḥammad-‘Alí,” Áqáy-i-Kalím, recounting this episode to Nabíl in Adrianople, has stated, “when apprized of this proposition, that he felt a strong desire to kill Mírzá Yaḥyá on the spot, and would have done so but for his fear of Bahá’u’lláh’s displeasure.
(Shoghi Effendi in God Passes By)
https://www.bahai.org/library/authoritative-texts/shoghi-effendi/god-passes-by/12#972283719