Reference for Sukkah 112:6

ויש אומרים משמרתו שוהה לבא ונכנס ישבב אחיו עמו ושימש תחתיו אע"פ ששכיני הרשעים לא נשתכרו שכיני בילגה נשתכרו שבילגה לעולם חולקת בדרום וישבב אחיו בצפון

Some however, say that the course [of Bilgah] was late in coming and [that of] Yeshbav its fellow entered in its place and served in their stead. Although the neighbors of the wicked are not rewarded the neighbors of were rewarded, since [after the imposition of the penalty, the course of] Bilgah always divided their shares in the south, while that of his brother Yeshbav did so in the north.

Jastrow