The Báb revealed the Dalá'il-i-Sab'ih (the “Seven Proofs”) while incarcerated in Mah-Ku. In it, He sets out the truth of His mission.
A collection of the Báb’s Writings can be read at the Bahá’í Reference Library. An extract from the Dalá'il-i-Sab'ih (the “Seven Proofs”) is shared below.
Thou hast asked concerning the fundamentals of religion and its ordinances: Know thou that first and foremost in religion is the knowledge of God. This attaineth its consummation in the recognition of His divine unity, which in turn reacheth its fulfillment in acclaiming that His hallowed and exalted Sanctuary, the Seat of His transcendent majesty, is sanctified from all attributes. And know thou that in this world of being the knowledge of God can never be attained save through the knowledge of Him Who is the Dayspring of divine Reality.
Rid thou thyself of all attachments to aught except God, enrich thyself in God by dispensing with all else besides Him, and recite this prayer:
Say: God sufficeth all things above all things, and nothing in the heavens or in the earth or in whatever lieth between them but God, thy Lord, sufficeth. Verily, He is in Himself the Knower, the Sustainer, the Omnipotent.
Regard not the all-sufficing power of God as an idle fancy. It is that genuine faith which thou cherishest for the Manifestation of God in every Dispensation. It is such faith which sufficeth above all the things that exist on the earth, whereas no created thing on earth besides faith would suffice thee. If thou art not a believer, the Tree of divine Truth would condemn thee to extinction. If thou art a believer, thy faith shall be sufficient for thee above all things that exist on earth, even though thou possess nothing.