Here is the authentic wording concerning the du`aa of the fasting person: '...until he breaks his fast..',the wording 'when he breaks his fast' being unauthentic -wallaahu a`lam.
[reference:'Irwaa.ul-Ghaleel' (no.921) of Shaikh al-Albaanee -rahimahullaah.]
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May Allaah reward by Aboo Talhah Dawud ibn Ronald Burbank. Aameen.