I heard the Messenger of Allah ﷺ say: When a Muslim supplicates for his absent brother the angels say: Amin, and may you receive the like.  

أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ يَقُولُ إِذَا دَعَا الرَّجُلُ لأَخِيهِ بِظَهْرِ الْغَيْبِ قَالَتِ الْمَلاَئِكَةُ آمِينَ وَلَكَ بِمِثْلٍ  

The Prophet ﷺ said: The supplication which gets the quickest answer is that made by one distant Muslim for another.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ أَسْرَعَ الدُّعَاءِ إِجَابَةً دَعْوَةُ غَائِبٍ لِغَائِبٍ  

The Prophet ﷺ said: Three supplications are answered, there being no doubt about them; that of a father, that of a traveller and that of one who has been wronged.  

أَنَّ النَّبِيَّ ﷺ قَالَ ثَلاَثُ دَعَوَاتٍ مُسْتَجَابَاتٌ لاَ شَكَّ فِيهِنَّ دَعْوَةُ الْوَالِدِ وَدَعْوَةُ الْمُسَافِرِ وَدَعْوَةُ الْمَظْلُومِ