Bab about Akhbari, Usuli and Shaykh Ahmad

"Now that you know the true significances of this world, know that, today, in the branch of the Isna Ashari, the divergencies have arrived at their summit. Certain ones, known under the name of Ousouli believe in the possession of the truth, because they have the science of Zenn (analogy), on the subject of which they all agree; others, known under the name of Akhbari believe they are in the truth because they do not accept the testimony of brilliant intelligence; others, known under the name of the fire Shaykh Ahmad, son of Zenn ed din-may God bless the dust of his tomb-believe they are in possession of the absolute and pure truth. They have not however understood the tenth (or one tenth?) of the sayings of this illustrious unitarian!"

The Bab (Kitab-i-Bayan Arabic)

There is no doubt that the absolute Truth, in the midst of all these divergences of the Isna 'Ashari sect, is found in one among them. 

The Bab (Kitab-i-Bayan Arabic)

https://bahai-library.com/pdf/b/bab_bayan_arabic_terry.pdf