חסידות אויף תהילים 137:1

And this is the behina of: “By the rivers of Babylon, there we sat, sat and wept” (Psalms 137:1)—this is the behina of the Babylonian Talmud, that was composed at the yeshivot (seminaries/houses of study), from which rivers are made, as stated. And hence: “and wept” — because one must cry beforehand, in the behina of: “and mixed (masakh) my drink with tears” (Psalms 102:10), as stated.