It seems that the “Hazon Gabriel” constitutes documentary evidence of the practice of teaching from a text copied on a plastered stone following a tradition found in the Old Testament.I am surprised that the essay has no reference to the Balaam Text from Tell Deir ‘Allā.
(By the way, have I mentioned that volume one of the texts translated for the More Old Testament Pseudepigrapha Project is in press and should be out in the next few months? This volume includes a translation of the Balaam Text by Edward Cook.)
Background on the Gabriel Revelation (Vision of Gabriel) is here and here and links.
UPDATE: Bad links now fixed. Sorry!