Alla Upanisad?

[Anshuman Pandey]

As I read through David Frawley's "God, Sages, and Kings," I came upon a 
reference to the Alla Upanisad. Frawley mentioned that it was probably 
composed after Islam had formally entered India, and I assume that it is a 
rather minor Upanisad, but I cannot find any books which offer more detailed 
information about it, nor can I find it listed in any collections of 
Upanisadic texts or in any library catalogues (at least those which I 
can access through this University's system). Does anyone know if such 
an Upanisad exists, and possibly where it may be found?

Thank you.

Anshuman Pandey