This is an allusion to Manyoshu #2265:
Asagasumi/ kaiya ga shita ni/
naku kawazu/ koe da ni kikaba/ ware koime ya mo.
(In the morning mist/
Under the silkworm nurdery/ A toad croaks.../ If only I could hear
our voice/ None of this yearning for you! Ueda Makoto).
It is also
a reference to Manyoshu #3818:
Asagasumi/ kaiya ga shita no/ naku
kawazu/ shinobitsutsu ari/ to tsugen ko mo ga mo.