He—may Allah have mercy on him—also says in his Nuniyya, “Al-Kāfiya al-Shāfiya”:

“Consider Harb and the consensus he transmitted …
Well done, young man of Kerman!”
(1)

It is important to point out that the section entitled “The Chapter on Professing the School,” together with its report of the early scholars’ creed, is likewise circulated as being from Imam Ahmad ibn Hanbal. This is the epistle that Ahmad ibn Jaʿfar al-Isṭakhrī claims to have received from Imam Ahmad. Ibn Abi Yaʿla reproduced the entire creed in his Tabaqāt al-Ḥanābila under al-Isṭakhrī’s biography.

Shaykh al-Islam Ibn Taymiyyah, however, showed that this epistle cannot be reliably ascribed to Imam Ahmad, saying:

“This creed is not authentically established from Imam Ahmad in these exact words. I examined three obscure chains of transmission for it, each containing unknown narrators, and the wording is that of Harb ibn Ismāʿīl, not that of Imam Ahmad. Those devoted to compiling Ahmad’s statements—such as Abū Bakr al-Khallāl in his Book of the Sunnah and other Iraqi scholars well acquainted with Ahmad’s works—do not mention it, nor is it transmitted by the recognised narrators of his words, especially given the size of this epistle, even though it has gained currency among many later writers.”
(2)

Al-Ḥāfiẓ al-Dhahabī likewise rejected the attribution of this epistle to Imam Ahmad. (3)