Thou hast asked about the infallibility of the ancient prophets. The Holy Manifestations uttered that which was revealed unto them and not that which they desired. They are the manifestation of “God warns you to beware of His Self” (Q 3:28), or rather, the Self of God that hath established the divine precepts. They are exalted above the recognition of others and sanctified from the vain imaginings of the people of doubts and idle fancies. Refer to the divine texts, which explicitly mention the Most Great Infallibility that is their right, whether in the verses of the Most Exalted One (the Bab), or in the clarifying verses of the Abha Beauty, such as the tablet of visitation for the Prince of Martyrs (Imam Husayn), upon him be salutations and praise.
As for the meaning of “Adam disobeyed” (Q 20:121) and the verse “what is past of thy sin and what is to come” (Q 48:2), this is a station in which the good works of the righteous are the misdeeds of the near ones, and “Thine existence is a sin to which no sin compareth.” A soft breath revealeth the mirror’s surface, and imaginary dust cloudeth the eye.
The Most Exalted One (the Bab) hath said, “In mine eyes, seeking the love of Thy nearness is like idolatry in the eyes of others.” If, God forbid, it can be said that seeking divine nearness is sinful and idolatrous, then the Holy Manifestations are not the manifestation of the Most Great Infallibility. We ask forgiveness of God for such a thought! They are infallible, protected, sanctified, and safe-guarded.
Abdu’l-Baha, Muntakhabati 6: 366-7. The line “Thine existence is a sin to which no sin compareth” is often quoted by Sufis without attribution. My thanks to Iskandar Hai for his help rendering the sentence beginning “A soft breath….”