Bible. Seeing Morgana coming around the dark side of Avalon, he quotes:
"'O moon of my delight that knows no wane -'" (Rise Of The Terran Empire, p. 526) (See here)
Ah, Moon of my Delight who know’st no wane,
The Moon of Heav’n is rising once again:
How oft hereafter rising shall she look
Through this same Garden after me — in vain!
-copied from here.
The Moon will look for "me" in vain either because I am dead or because my old self has ended. The Moon who know'st no wane is the Absolute or Eternal.
We read the Rubaiyat in English translation. I imagine that Ferune has read it in Anglic translation rather than in the original Persian?