I heard that the earlier source of the tafseer of “al kawthar” being about Fatima al Zahra was Fakhr al Din al Razi (Sunni) but do we have earlier shia sources, ahadith, tafseer that show that it is shia interpretation?

Scholars of tafsir mention a hadith from Ibn Abbas- in which he says one of the pagans used to call the prophet Abtar – then the Quran says your enemies are abtar.

Fakhr al-Razi says it is the progeny of the prophet. Other scholars have understood it differently.

However just the hadith of Ibn Abbas is clear to understand that the reference is to lady Fatima.

The fact that a Sunni is narrating a hadith in praise of Lady Fatima makes it greater in proof. We prove the Imama and greatness of Ahlulbayt from their books. There is no issue with that. This is admission from them, so it can be accepted.