Baha'u'llah - Bayan is not abrogated
"I swear by God that if any one of the People of the Bayan were to mention that the Book [the Bayan] is abrogated, may God smash the mouth of the speaker and the calumniator, and by him who holds my soul and myself in his hands one letter from the Bayan is the most loved with me than all that are in the heavens and on the earth"
(1862 Letter of Bahá during the Baghdad Period).
“I swear by God that if any of the people of the Bayan [Babis] was to mention that the Book [Bayan] is abrogated, may God break the mouth of the speaker and the calumniator.”
Azal’s Notes, pp. 165, 599, 1055, 1056, 1086, Letter No. One of Baha. See appendix II, #4.
The Baha'i Faith: Its History and Teachings, by William Miller