Reference for Shabbat 283:15

וחכמים אומרים אין המדומע מדמע אלא לפי חשבון

states: If money is lying on a cushion, one shakes the cushion, and it falls off. Whereon Rabbah b. Bar Hanah said in R. Johanan's name: They learnt this only if it [the cushion] is required for itself; but if its place is required, one removes it while it [the money] is upon it. And since the second clause means that it is required for itself, the first clause too means that it is required for itself.

Jastrow