Rashi on Numbers 36:3/רש"י על במדבר ל״ו:ג׳

1ונוסף על נחלת המטה AND IF THEY BECOME WIVES TO ANY SONS OF THE OTHER TRIBES … THEN WILL THEIR INHERITANCE] BE ADDED TO THE INHERITANCE OF THE TRIBE [WHEREUNTO THEY SHALL BELONG] — for her son will be her heir and the son reckons his pedigree after his father’s tribe.