Letters of the Bab to Mullā Ṣādiq Muqaddas Khurāsānī,
Ism-Allāh al-Asdaq (d. Hamadan 1889 CE)
Text above as cited in Afnan `Ahd-i A`la (Oxford: Oneworld, 2000), p. 101.
The issue of the changing of the Shi`i Islamic adhan (Call to prayer) is commented upon by the Bāb himself in the beginning of an early Arabic letter to Mulla Ṣādiq-i Muqaddas-i Khurāsānī who was himself involved in the Shiraz episode as described in the Dawn-Breakers or Tarkh-i Zarandi (see below) and in a Times article of 19/11/1843 (p.3). In this early letter the Khasā’l-i sab`a seems to be referred to as part of (?) a currently unknown Kitab al-mulūk ("Book of the Kings") and Mulla Ṣādiq Muqaddas-i Khurasānī is advised to make a fearless proclamation of the position of the Bab :
A Letter of the Bāb to his disciple Mulla Ṣādiq Muqaddas-i Khurasānī
Second Letter to Mullā Ṣādiq [Muqaddas] Khurāsānī
Translation Stephen Lambden
In the Name of God, the Merciful, the Compassionate.
 The Remembrance of God (Dhikr Allah) hath mentioned the yellow leaf (l'l-waraqat al-sufrā') nigh the right-hand side of the Mount [Sinai] (al-ṭūr), [saying] `No God is there except Him'.  Say: `Go ye out after Me!'.  We indeed previously sent down unto thee a letter (kitāb an) wherein were expository verses (āyāt bayyinat) from Us [addressed to] the people to the end that they might hearken.  We have indeed heard that today, after thy dwelling in that region [presumably Shiraz], thou did follow the base passions of such as were unaware of the decree of the Baqiyyat Allāh (Remnant of God) through his servant (`abd = the Bab) `Alī [`the Elevated One], the Wise One (al-ḥakīm) and did not publicly (jahrat) carry out [communicate] the decree of God (ḥukm Allāh) out of fear that the people would hear the verses of God (āyāt Allāh).  So recite Our verses every day amongst the people, not merely to the extent of a mustard seed out of fear.  Even if God commanded the like of that [public disclosure] such is indeed the Truth [despite the fact that] the people would cry out [in protest!
 We indeed wrote unto the believers that they should make mention of the Dhikr- Allāh (Remembrance of God) in the adhān ("Call to Prayer") according to a decree (ḥukm) that We sent down in the Kitāb al-Mulūk ("Book of the Kings").  So lift ye up [your voice] publicly (jahrat an)! [in obedience to] the decree of God (ḥukm Allāh), perchance thou will achieve success.
 O Thou man (al-rijal)! [Mulla Ṣādiq] Perform your devotions in the mosque (al-majid) [the Shiraz house of the Bāb] for therein were the verses (al-āyāt) from thy Lord sent down.  And instruct therein in Our verses (āyāt) with justice (bi’l-`adl) to the end that thou might assuredly be numbered among such as have attained.  It [the Shiraz house] is the first house (bayt) wherein the Book (al-kitāb) was revealed and therein indeed did the men of the holy land (rijāl arḍ al-muqaddasa) [Shaykhis from Iraq] come to believe.  They were assuredly among the forerunners (al-sābiqūn).  And it [the Shiraz house of the Bāb] is indeed a moque (al-masjid).  It was assuredly so established with justice (bi’l-`adl) in accordance with the ordinance of thy Lord (ḥukm rabbika) though it was, in the beginning, (fi’l-awwāl) the house [synagogue] of the Jews [Jewish community] (bayt al-yahūd).  And now it is indeed inscribed in the Book of God (al-kitāb Allāh) as the “Holy Land” (arḍ al-muqaddasa).
 And We did indeed send down a letter (kitāban) unto the land of Kirmān which was dispatched the very moment it was revealed .....
The Episode of the adhān ("Call to Prayer") in Shiraz 1845 CE.
The passage in Para I:8-9 above evidently relates to an early episode surrounding the incorporation of reference to the Bab as servant of the Dhikr-Allāh (Remembrance of God) into the Shi`i Islamic adhān ("Call to Prayer") in Shiraz. The Bab states that this directive was contained in the Kitāb al-Mulūk ("Book of the Kings") which may be indicative of a work incorporating or another name for the Khasā’il-i sab`a. Whatever the case, Mulla Ṣādiq is clearly rebuked for not reciting publicly the words or new adhān of the Bab. He should be fearless and ignore the clamor of the people. The Zarandi-Dawn-Breakers account of Mulla Ṣādiq's role in the Shiraz episode of the new adhan does not reflect the contents of the above letter but presents him as an eager devotee ready to immediately incorporate the new addition to the adhan. Perhaps, in reality, Mulla Ṣādiq gradually summoned up the courage to adopt the call to prayer to reference the Bab as servant of the Dhikr-Allah.
Muhammad Nabil-i Zarandi (d. 1892 CE) on the Khasā’l-i sab`a
In Shoghi Effendi's redaction of the Tarikh or History of Nabil-i Zarandi entitled the Dawn-Breakers (ch. VII see URL above) it is recorded :
"The Bab then delivered into his [Quddus'] hands a letter He had written to Haji Mirza Siyyid Ali, His maternal uncle, in which He had informed him of His safe return to Bushihr. He also entrusted him with a copy of the Khasa'il-i-Sab'ih, (1) a treatise in which He had set forth the essential requirements from those who had attained to the knowledge of the new Revelation and had recognised its claim. As He bade Quddus His last farewell, He asked him to convey His greetings to each of His loved ones in Shiraz...
"The next person whom Quddus met in Shiraz [in 1845 CE] was Ismu'llahu'l-Asdaq, Mulla Sadiq-i-Khurasani, to whom he entrusted the copy of the Khasa'il-i-Sab'ih, and stressed the necessity of putting into effect immediately all its provisions. Among its precepts was the emphatic injunction of the Bab to every loyal believer to add the following words to the traditional formula of the adhan: (1) "I bear witness that He whose name is Ali-Qabl-i-Muhammad (2) is the servant of the Baqiyyatu'-llah."(3) Mulla Sadiq, who in those days had been extolling from the pulpit-top to large audiences the virtues of the imams of the Faith, was so enraptured by the theme and language of that treatise that he unhesitatingly resolved to carry out all the observances it ordained. Driven by the impelling force inherent in that Tablet, he, one day as he was leading his congregation in prayer in the Masjid-i-Naw, suddenly proclaimed, as he was sounding the adhan, the additional words prescribed by the Bab. The multitude that  heard him was astounded by his cry. Dismay and consternation seized the entire congregation. The distinguished divines, who occupied the front seats and who were greatly revered for their pious orthodoxy, raised a clamour, loudly protesting: "Woe betide us, the guardians and protectors of the Faith of God! Behold, this man has hoisted the standard of heresy. Down with this infamous traitor! He has spoken blasphemy. Arrest him, for he is a disgrace to our Faith." "Who," they angrily exclaimed, "dared authorise such grave departure from the established precepts of Islam? Who has presumed to arrogate to himself this supreme prerogative?"...