Parashas Shemos · Passuk 2:22
Chabad.org — English translation + Rashi
Torah Temimah points to Gittin (laws of personal names) (verified).
English: “Gershom” — from here [we learn] that the name Gershom is distinct from the name Gershon, with practical consequence for names in gittin.
In context: See the cited source for the full section.
Custom
Chazal note that Gershom and Gershon are distinct names, a distinction that matters for the exactitude of names in a get.