Abu Hurairah (May Allah be pleased with him) reports,
Rasulullah (sallallaho alaihi wa sallam) declared,
'Three men whose dua is never rejected (by Allah) are:
the fasting person until he breaks his fast
(in another narration, when he breaks fast),
the just ruler and the one who is oppressed.
'[Ahmad, at-Tirmidhi - Hasan]