Rashi on Exodus 6:23/רש"י על שמות ו׳:כ״ג

1אחות נחשון THE SISTER OF NAASHON — Hence they (the Rabbis) learned (i.e. from the fact that Scripture states who her brother was when it mentions her marriage to Aaron) that he who is about to take a wife should strictly investigate who her brothers are (Bava Batra 110a).