Rashi on Numbers 1:18/רש"י על במדבר א׳:י״ח

1ויתילדו על משפחותם THEY DECLARED THEIR PEDIGREES AFTER THEIR FAMILIES — They brought the records of their pedigree and witnesses to confirm the prevalent presumption regarding their parentage, so that each might establish his pedigree with regard to the particular tribe (cf. Yalkut Shimoni on Torah 684).