Mishkat al-Masabih 2250
He reported God’s messenger as saying, “Three supplications are answered, there being no doubt about them:
that of a parent, that of a traveller, and that of one who has been wronged.” 

Tirmidhi, Abu Dawud and Ibn Majah transmitted it.
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 
" ثَلَاثُ دَعَوَاتٍ مُسْتَجَابَاتٍ لَا شَكَّ فِيهِنَّ: دَعْوَةُ الْوَالِدِ وَدَعْوَةُ الْمُسَافِرِ وَدَعْوَةُ الْمَظْلُومِ ". رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَابْنُ مَاجَهْ