Commentary for Berakhot 125:1

ואימא הר הבית דאסור במנעל לילפא ממנעל אבל (ב"ה) דשרי במנעל אדיליף ממנעל ולהיתר נילף מקפנדריא ולאסור

and I say that with reference to the Temple Mount where [the wearing of] a shoe is forbidden, let one derive [the prohibition against expectoration] from a shoe; but with reference to the Synagogue where one is permitted [to wear] shoes, instead of deriving permission [to expectorate, by analogy] from a shoe, let him derive a prohibition [against expectoration, by analogy] from the short cut !

Abraham Cohen Footnotes to the English Translation of Masechet Berakhot