I'm not quite sure but it seems that reciting Nade Ali kabeer is shirk as we are calling Ali a.s for help rather than Allah. I know the concept of tawassul and in that we can help frok Allah but through the means of someone else but in this dua we are asking help directly from hHazrat Ali and not Allah. Can you please explain this? Also where has this dua came from? How can we know that this is an authentic dua?

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Prophet (sawa) recited this Dua at the battle of Uhud and also Khaybar.

It has been mentioned in various books of Hadith including Biharul Anwar