From ˁl. For additional meanings see s.v. It should be noted that in JBA when used as a verbal complement (see DJBA 71:II) על itself is generally much more frequently found.
This form may exist as early as the incantation from Uruk in cuneiform script: di-a-ba-ba-ˀ, "of the door", but it is uncertain.
The two LJLA examples cited above are essentially the only ones in that dialect, and both are forms known to the scribes from talmudic passages.