Al-Adab Al-Mufrad, Book 1, Hadith 32 (English) ⓘ

Abu Hurayra reported that the Prophet, may Allah bless him and grant him peace, said, "Three supplications are answered without a doubt: the supplication of someone who is oppressed, the supplication of someone on a journey, and the supplication of parents for their children."

حَدَّثَنَا مُعَاذُ بْنُ فَضَالَةَ، قَالَ‏:‏ حَدَّثَنَا هِشَامٌ، عَنْ يَحْيَى هُوَ ابْنُ أَبِي كَثِيرٍ، عَنْ أَبِي جَعْفَرٍ، أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ يَقُولُ‏:‏ قَالَ النَّبِيُّ صلى الله عليه وسلم‏:‏ ثَلاَثُ دَعَوَاتٍ مُسْتَجَابَاتٌ لَهُنَّ، لاَ شَكَّ فِيهِنَّ‏:‏ دَعْوَةُ الْمَظْلُومِ، وَدَعْوَةُ الْمُسَافِرِ، وَدَعْوَةُ الْوَالِدِيْنِ عَلَى وَلَدِهِمَا‏.‏