Midrash about hitting thumb with hammer to show that we should not take vengeance on another Jew

Question

Rav Zamir Cohen recounted a Midrash for parashat Vi-Yi’hi, which talks about how we need to have אהבת חינם since כל יהודי ערב זה בזה

To buttress the point he says there is a midrash, which says that if you bang your thumb with a hammer, the hurt hand won’t attack the other (likewise, we should not get angry at a fellow Jew).

However, I can’t find the source of this midrash. Any help?

Answer 1

The source is the Y'rushalmi (N'darim 9:4), speaking about the prohibition to take revenge against a fellow Jew ("Do not take revenge or bear a grudge against the children of your people" Vayikra 19:18):

היך עבידא הוה מקטע קופד ומחת סכינא לידוי תחזור ותמחי לידיה

Translation:

What is this case [comparable to]? If someone was cutting a piece of meat, and the knife fell onto his hand. Would he then bring down the knife again on his [other] hand [in revenge]?