The Báb “never named” a “successor or vicegerent” or “an interpreter of His teachings”

A successor or vicegerent the Báb never named, an interpreter of His teachings He refrained from appointing. So transparently clear were His references to the Promised One, so brief was to be the duration of His own Dispensation, that neither the one nor the other was deemed necessary. All He did was, according to the testimony of ‘Abdu’l‑Bahá in “A Traveller’s Narrative,” to nominate, on the advice of Bahá’u’lláh and of another disciple, Mírzá Yahyá, who would act solely as a figurehead pending the manifestation of the Promised One, thus enabling Bahá’u’lláh to promote, in relative security, the Cause so dear to His heart. 

- Shoghi Effendi  (Chapter 2, ‘God Passes By’)

The Báb “assiduously prepared” some of His disciples “to expect the imminent Revelation” of Baha’u’llah

Some of His disciples the Báb assiduously prepared to expect the imminent Revelation. Others He orally assured would live to see its day. To Mullá Báqir, one of the Letters of the Living, He actually prophesied, in a Tablet addressed to him, that he would meet the Promised One face to face. To Sayyáḥ, another disciple, He gave verbally a similar assurance. Mullá Husayn He directed to Tihrán, assuring him that in that city was enshrined a Mystery Whose light neither Hijáz nor Shíráz could rival. Quddús, on the eve of his final separation from Him, was promised that he would attain the presence of the One Who was the sole Object of their adoration and love. To Shaykh Hasan-i-Zunúzí He declared while in Máh-Kú that he would behold in Karbilá the countenance of the promised Husayn. On Dayyán He conferred the title of “the third Letter to believe in Him Whom God shall make manifest,” while to ‘Azím He divulged, in the Kitáb-i-Panj-Sha‘n, the name, and announced the approaching advent, of Him Who was to consummate His own Revelation. 

- Shoghi Effendi  (Chapter 2, ‘God Passes By’)

The Báb made “a Lesser Covenant… with the entire body of His followers concerning” Baha’u’llah

It had now to be supplemented by a Lesser Covenant which He felt bound to make with the entire body of His followers concerning the One Whose advent He characterized as the fruit and ultimate purpose of His Dispensation. Such a Covenant had invariably been the feature of every previous religion. It had existed, under various forms, with varying degrees of emphasis, had always been couched in veiled language, and had been alluded to in cryptic prophecies, in abstruse allegories, in unauthenticated traditions, and in the fragmentary and obscure passages of the sacred Scriptures. In the Bábí Dispensation, however, it was destined to be established in clear and unequivocal language, though not embodied in a separate document. Unlike the Prophets gone before Him, Whose Covenants were shrouded in mystery, unlike Bahá’u’lláh, Whose clearly defined Covenant was incorporated in a specially written Testament, and designated by Him as “the Book of My Covenant,” the Báb chose to intersperse His Book of Laws, the Persian Bayán, with unnumbered passages, some designedly obscure, mostly indubitably clear and conclusive, in which He fixes the date of the promised Revelation, extols its virtues, asserts its pre-eminent character, assigns to it unlimited powers and prerogatives, and tears down every barrier that might be an obstacle to its recognition. “He, verily,” Bahá’u’lláh, referring to the Báb in His Kitáb-i-Badí‘, has stated, “hath not fallen short of His duty to exhort the people of the Bayán and to deliver unto them His Message. In no age or dispensation hath any Manifestation made mention, in such detail and in such explicit language, of the Manifestation destined to succeed Him.” 

- Shoghi Effendi  (Chapter 2, ‘God Passes By’)