Rashi on Numbers 11:10/רש"י על במדבר י״א:י׳

1בכה למשפחתיו [THEN MOSES HEARD THE PEOPLE] WEEP THROUGHOUT THEIR FAMILIES — i.e. the members of each family gathered together and wept in order to display their discontent in public. Our Rabbis, however, said that למשפחתיו means “the people wept because of family affairs” — because of the intermarriage of blood-relaltives that had been forbidden to them (Sifrei Bamidbar 90; Yoma 75a).