"Sandhyabasha"

[thompson at jlc.net]

I'm pretty sure that the source of Waldman's remarks is Eliade's "Yoga:
Immortality and Freedom", since it refers briefly to sandhyA-bhASA [in the
Kyoto-Harvard transcription system], and since all of the Beats were
reading Eliade [besides the book on yoga, there was a lot of interest in
his book on Shamanism].

You might check out the now classic study of S. Das Gupta [upon which
Eliade depended greatly], "Obscure Religious Cults" [3rd edit., 1969], who
by the way suggests that the alternation between sandhA- [i.e.,
"intentional" language] and sandhyA- [i.e., "twilight" language; cf.
"sandhi"] is not due to scribal error but to intentional double-sense.

There is a lot of more recent literature on this, which specialists might
want to recommend, but these two books seem to me to have the best chance
of being the ones that Waldman, Kerouac, et al., were familiar with.

Best wishes
George Thompson