Kiddushin 71 - Family Conflict

Rav Yehudah was not sure how to find a genealogically fit wife for his son. Ulla said to him, - do we know from where we ourselves come? We might be descended from those "... who lie upon beds of ivory and defile their couches ." Rather, go after silence, that is, find family whose members are quiet and peaceable.

If you see two families in conflict with one another, you can assume that there is some genealogical flaw in one of them, and because of that flaw Heaven will not allow one of them to cleave to the other.