“The tendency of these writings to enumerate celestial beings and their names is sometimes reminiscent of the catalogues to be found in the Pistis Sophia and other gnostic (Mandaean) texts of a later period. Isaac Cohen, who preserved for us many such lists and enumerations, attributed them to a particular group of kabbalists who had not walked the “royal road” followed by the others.
The source of these lists (as distinct from the demonological speculations discussed previously) is said to be a source he called the Book of Rab Hammai, which he claims to have found in Provence in three copies: one in Narbonne, in the possession of the aforementioned anonymous Hasid, and two in Aries.
Here we find ourselves in a very curious situation. The Book of Hammai is lost; Moses of Burgos, Isaac’s disciple, still quoted further catalogues of archons of a gnostic character; the name appears in several other writings that in all probability also originated in Provence.
But no historical personage by this name is known. Whether the Amora Hamma ben Hanina has been transformed into a pseudepigraphic author, or the name Rahmai, , known to us from the Bahir has perhaps become a Rab Hammai, or whether we are simply dealing with a new fiction, can no longer be determined.
In the most important of the extant texts, Hammai appears as a speculative author of the eleventh or twelfth century who already relied upon pseudepigraphic kabbalistic writings circulating in the name of Hai Gaon (d.1040). In addition to a “Book of the Unity,” Sefer ha-Yihud, from which only some quotations remain, we have a small tract entitled Sefer ha-‘Iyyun, “Book of the Speculation” (or “Contemplation”), preserved in numerous manuscripts.”
Gershom Scholem, Origins of the Kabbalah, pp. 310-1.