Reference for Chullin 178:1

שיעורא בעינן ועבודת כוכבים כתותי מכתת שיעורא הכא כל מה דמכתת מעלי לכסוי:

a minimum size is prescribed, and since it has been used for idolatry it is regarded as though the size were diminished,<span class="x" onmousemove="('comment',' Lit., 'broken up' and reduced below the minimum; this in accordance with the Rabbinic dictum: Whatsoever is to be destroyed is deemed destroyed forthwith.');">¹</span>

Jastrow