The Kitáb-i-Íqán : - “occupies a position unequalled by any work in the entire range of Bahá’í literature, except the Kitáb-i-Aqdas”

A model of Persian prose, of a style at once original, chaste and vigorous, and remarkably lucid, both cogent in argument and matchless in its irresistible eloquence, this Book, setting forth in outline the Grand Redemptive Scheme of God, occupies a position unequalled by any work in the entire range of Bahá’í literature, except the Kitáb-i-Aqdas, Bahá’u’lláh’s Most Holy Book. Revealed on the eve of the declaration of His Mission, it proffered to mankind the “Choice Sealed Wine,” whose seal is of “musk,” and broke the “seals” of the “Book” referred to by Daniel, and disclosed the meaning of the “words” destined to remain “closed up” till the “time of the end.” 

- Shoghi Effendi (‘God Passes By’, chapter 8)

1862: The revelation of “the Kitáb-i-Íqán (Book of Certitude), revealed within the space of two days and two nights” – a “fulfillment of the prophecy of the Báb, …to complete the text of the unfinished Persian Bayán”

Foremost among the priceless treasures cast forth from the billowing ocean of Bahá’u’lláh’s Revelation ranks the Kitáb-i-Íqán (Book of Certitude), revealed within the space of two days and two nights, in the closing years of that period (1278 A.H.–1862 A.D.). It was written in fulfillment of the prophecy of the Báb, Who had specifically stated that the Promised One would complete the text of the unfinished Persian Bayán, and in reply to the questions addressed to Bahá’u’lláh by the as yet unconverted maternal uncle of the Báb, Hájí Mírzá Siyyid Muhammad, while on a visit, with his brother, Hájí Mírzá Hasan-‘Alí, to Karbilá. 

- Shoghi Effendi (‘God Passes By’, chapter 8)