The source gives Taghlib as another verb-pattern example, beginning with the prefix letter tāʾ.
مَرَرْتُ بِتَغْلِبَ. — I passed by (the tribe of) Taghlib.
بِـ is the preposition; تَغْلِبَ is genitive with fatḥa because it is being used here as the proper name of a tribe.
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Diptote Causes — Verb Patterns and Their Conditions
The source gives Taghlib as another verb-pattern example, beginning with the prefix letter tāʾ.
مَرَرْتُ بِتَغْلِبَ. — I passed by (the tribe of) Taghlib.
بِـ is the preposition; تَغْلِبَ is genitive with fatḥa because it is being used here as the proper name of a tribe.