I had sohoor intending that I was following my mobile app of athan time, then double checked IAR and discovered that fajer passed according to IAR time table. I committed to IAR schedule after that but my neighbor didnt know about this difference until the end of ramadhan. Do I need to re-fast? IAR has around a 15 min lead on fajer time than Ibad rahman and the athan app.

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You do not need to re-fast any day since Fajir time tables are all estimated and you did not know at that time of the difference.