Grand Vizir’s representative delivered the king’s order for Bahá’u’lláh’s release from Síyáh-Chál

With such overwhelming testimonies establishing beyond the shadow of a doubt the non-complicity of Bahá’u’lláh, the Grand Vizir, after having secured the reluctant consent of his sovereign to set free his Captive, was now in a position to dispatch his trusted representative, Hájí ‘Alí, to the Síyáh-Chál, instructing him to deliver to Bahá’u’lláh the order for His release. The sight which that emissary beheld upon his arrival evoked in him such anger that he cursed his master for the shameful treatment of a man of such high position and stainless renown. Removing his mantle from his shoulders he presented it to Bahá’u’lláh, entreating Him to wear it when in the presence of the Minister and his counsellors, a request which He emphatically refused, preferring to appear, attired in the garb of a prisoner, before the members of the Imperial government. 

- Shoghi Effendi  (‘God Passes By’)

Factors that effected Bahá’u’lláh’s “ultimate deliverance” from Síyáh-Chál

Now that He [Bahá’u’lláh] had been invested, in consequence of that potent dream, with the power and sovereign authority associated with His Divine mission, His deliverance from a confinement that had achieved its purpose, and which if prolonged would have completely fettered Him in the exercise of His newly-bestowed functions, became not only inevitable, but imperative and urgent. Nor were the means and instruments lacking whereby his emancipation from the shackles that restrained Him could be effected. 

• The persistent and decisive intervention of the Russian Minister, Prince Dolgorouki, who left no stone unturned to establish the innocence of Bahá’u’lláh;
• the public confession of Mullá Shaykh ‘Alíy-i-Turshízí, surnamed ‘Azím, who, in the Síyáh-Chál, in the presence of the Hájibu’d-Dawlih and the Russian Minister’s interpreter and of the government’s representative, emphatically exonerated Him, and acknowledged his own complicity; 
• the indisputable testimony established by competent tribunals; 
• the unrelaxing efforts exerted by His own brothers, sisters and kindred,—all these combined to effect His ultimate deliverance from the hands of His rapacious enemies. 
• Another potent if less evident influence which must be acknowledged as having had a share in His liberation was the fate suffered by so large a number of His self-sacrificing fellow-disciples who languished with Him in that same prison. For, as Nabíl truly remarks, “the blood, shed in the course of that fateful year in Tihrán by that heroic band with whom Bahá’u’lláh had been imprisoned, was the ransom paid for His deliverance from the hand of a foe that sought to prevent Him from achieving the purpose for which God had destined Him.” 

- Shoghi Effendi  (‘God Passes By’)

Bahá’u’lláh’s exile began two months after His spiritual experience in the Siyáh-Chál

Two months after that year was born, Bahá’u’lláh, the purpose of His imprisonment now accomplished, was released from His confinement, and set out, a month later, for Baghdád, on the first stage of a memorable and life-long exile which was to carry Him, in the course of years, as far as Adrianople in European Turkey, and which was to end with His twenty-four years’ incarceration in ‘Akká. 

- Shoghi Effendi  (God Passes By, chapter 7)

Bahá’u’lláh’s imprisonment in the Siyáh-Chál “lasted for a period of no less than four months in the middle of which” He experienced “the first stirrings of God’s Revelation within His soul”

The attempt on the life of NAsiri’d-Dín Sháh, as stated in a previous chapter, was made on the 28th of the month of Shavvál, 1268 A.H., corresponding to the 15th of August, 1852. Immediately after, Bahá’u’lláh was arrested in Níyávarán, was conducted with the greatest ignominy to Tihrán and cast into the Síyáh-Chál. His imprisonment lasted for a period of no less than four months, in the middle of which the “year nine” (1269), anticipated in such glowing terms by the Báb, and alluded to as the year “after Hín” by Shaykh Ahmad-i-Ahsá’í, was ushered in, endowing with undreamt-of potentialities the whole world. 

- Shoghi Effendi  (God Passes By, chapter 7)

A “slow and gradual” process through which “the effulgence of so dazzling a Revelation was unfolded to the eyes of men”: - “A period of no less than ten years had to elapse”

The process whereby the effulgence of so dazzling a Revelation was unfolded to the eyes of men was of necessity slow and gradual. The first intimation which its Bearer received did not synchronize with, nor was it followed immediately by, a disclosure of its character to either His own companions or His kindred. A period of no less than ten years had to elapse ere its far-reaching implications could be directly divulged to even those who had been intimately associated with Him—a period of great spiritual ferment, during which the Recipient of so weighty a Message restlessly anticipated the hour at which He could unburden His heavily laden soul, so replete with the potent energies released by God’s nascent Revelation. All He did, in the course of this pre-ordained interval, was to hint, in veiled and allegorical language, in epistles, commentaries, prayers and treatises, which He was moved to reveal, that the Báb’s promise had already been fulfilled, and that He Himself was the One Who had been chosen to redeem it. A few of His fellow-disciples, distinguished by their sagacity, and their personal attachment and devotion to Him, perceived the radiance of the as yet unrevealed glory that had flooded His soul, and would have, but for His restraining influence, divulged His secret and proclaimed it far and wide. 

- Shoghi Effendi  (God Passes By, chapter 6)