במדבר, פרק ב׳, פסוק ה׳

The arrangement of the Israelite camp in the wilderness was deeply rooted in family ties. Leah had five sons who served as leaders of these tribal groupings, and they were divided into two main camps. Reuben, the eldest, led one group alongside Gad, the firstborn of Zilpah. Meanwhile, Judah took the lead of another. Because Judah was positioned at the front of his group, his younger brothers, Issachar and Zebulun, were stationed right beside him [חזקוני].

The description of their encampment indicates that these younger siblings were placed closely alongside Judah [ביאור שטיינזלץ, אבן עזרא, נתינה לגר]. Yet, the precise way their position is recorded does more than just group them together; it pinpoints Issachar's exact physical location within the formation. Rather than merely trailing somewhere in the same camp, Issachar was stationed immediately following Judah, serving as the direct middle link before the third tribe in their shared group [אבן עזרא, אבי עזר].