Reference for Chullin 96:2

בשוקא דרבנן חזי הנך דקיימן כנדי כנדי ולא אמר להו ולא מידי

R'Ammi and R'Assi were once passing through the market place of Tiberias when they saw lungs covered with large and hard lumps, and they said nothing to them [the butchers] about it.

Jastrow