One of Baha’u’llah’s bitterest enemies by the name of Shaykh 'Abdu'l-Husayn was sent by the Shah of Persia to Karbila (near Baghdad) to carry out the repair of the Muslim holy sites. He invited all ranks of clergy to a conference held at his home. There he forcefully condemned Baha'u'llah's activities, accused Him of destroying the Faith of Islam, and demanded that holy war should be proclaimed against the Babis of ‘Iraq. The body of the divines approved. However, the leading mujtahid  of the Shi’ah community, Shaykh Murtiday-i-Ansari, a man of justice and piety, refused to sanction their evil plans and arose and abruptly left the meeting.
Some time before this, Baha'u'llah had invited Shaykh 'Abdu'l-Husayn [the one who had called the conference of the divines] to meet Him face to face so that the truth of His Cause might be established. But the Shaykh, who had accepted the invitation at first, was afraid to meet the challenge and did not appear at the appointed place.
The conference of the divines decided to send a representative to Baha'u'llah to put certain questions to Him, designed to establish the truth of His Mission. The person they chose for this mission was a devout and high-minded cleric by the name of Haji Mulla Hasan-i-'Ammu. This Haji requested the assistance of a Prince in Baghdad, who was a friend and admirer of Baha'u'llah and had visited His home, to arrange for an interview with Baha’u’llah. When the appointed day came, the prince took Haji Mulla Hasan personally to the house of Baha'u'llah.
No sooner had Haji Mulla Hasan presented himself to Baha'u'llah than he discovered the ocean of His utterance surging before him and saw himself as a mere drop compared to the vastness of Baha’u'llah's knowledge. Having had his questions answered with brilliance and simplicity, he then ventured to inform Baha'u'llah that "The 'ulama recognize without hesitation and confess the knowledge and virtue of Bahá'u'lláh, and they are unanimously convinced that in all learning he has no peer or equal; and it is also evident that he has never studied or acquired this learning; but still the 'ulama say, 'We are not contented with this; we do not acknowledge the reality of his mission by virtue of his wisdom and righteousness. Therefore, we ask him to show us a miracle in order to satisfy and tranquilize our hearts.'" (Abdu'l-Baha, Some Answered Questions, p. 28)
Bahá'u'lláh replied, "Although you have no right to ask this, for God should test His creatures, and they should not test God, still I allow and accept this request. But the Cause of God is not a theatrical display that is presented every hour, of which some new diversion may be asked for every day. If it were thus, the Cause of God would become mere child's play. (ibid)
"The ulamas must, therefore, assemble, and, with one accord, choose one miracle, and write that, after the performance of this miracle they will no longer entertain doubts about Me, and that all will acknowledge and confess the truth of My Cause. Let them seal this paper, and bring it to Me. This must be the accepted criterion: if the miracle is performed, no doubt will remain for them; and if not, We shall be convicted of imposture." (ibid)
The learned man, Hasan 'Amu, rose and replied, "There is no more to be said"; he then kissed the knee of the Blessed One although he was not a believer, and went. He gathered the 'ulama and gave them the sacred message. They consulted together and said, "This man is an enchanter; perhaps he will perform an enchantment, and then we shall have nothing more to say." Acting on this belief, they did not dare to push the matter further. (ibid, p. 29)
Haji Mulla Hasan conveyed this decision to Baha'u'llah through the Prince who had arranged his meeting with Him. Upon hearing this news, Baha'u'llah is reported to have said:
“We have, bough this all-satisfying, all-embracing message which We sent, revealed and vindicated the miracles of all the Prophets, inasmuch as We left the choice to the 'ulamas themselves, undertaking to reveal whatever they would decide upon.”(Shoghi Effendi, God Passes By)
(Adapted from The Revelation of Baha’u’llah, by Adib Taherzadeh volume 1, and Stories of Baha’u’llah and Some Notable Believers by Kiser Barnes)
 A Muslim Doctor of Law. The highest rank of divine within Shi’ah Islam. One who has the power to make authoritative decisions on points of law in the name of the Hidden Imam]