Reference for Sukkah 48:4

ורבנן אי כתב בספר כדקאמרת השתא דכתיב ספר לספירת דברים בעלמא הוא דאתא

And the Rabbis? If Scripture had written "In a scroll", [it would be] as you say, but now that it is written "a scroll" it refers to the recital of the words.

Jastrow