وَإِنْ خِفْتُمْ شِقَاقَ بَيْنِهِمَا
If you fear discord between the two of them.
The expression “baynihimā” indicates the between-ness or relational location of the dispute between two spouses. The commentary considers this sort of construction while discussing association and predicational relations.
The instructional point is linguistic rather than a treatment of the verse's legal implications: an event can be related to its locus or relational setting, which is distinct from directly naming its agents.