'Abdullah ibn 'Amr reported that the Prophet, may Allah bless him and grant him peace, said, "The swiftest supplication to be answered is the supplication of someone for another person who is not present."  

عَنِ النَّبِيِّ ﷺ قَالَ أَسْرَعُ الدُّعَاءِ إِجَابَةً دُعَاءُ غَائِبٍ لِغَائِبٍ  

Abu Bakr as-Siddiq was heard to say, "The supplication of a brother in Allah is answered."  

أَنَّهُ سَمِعَ أَبَا بَكْرٍ الصِّدِّيقَ رَضِيَ اللَّهُ عَنْهُ إِنَّ دَعْوَةَ الأَخِ فِي اللهِ تُسْتَجَابُ  

Safwan ibn 'Abdullah ibn Safwan, who was married to the daughter of Abu'd-Darda', said, "I visited them in Syria and found Umm ad-Darda' in the house, but not Abu'd-Darda'. She asked, 'Are you intending to go on hajj this year?' 'Yes,' I replied. She said, 'Make supplication to Allah and ask for good for us. The Prophet, may Allah bless him and grant him peace, said, "The supplication of a Muslim man for his absent brother is answered. At his head there is a guardian angel. Whenever he asks Allah to give his brother good, the angel says, 'Amen, and may you have the same.'"' I met Abu'd-Darda' in the market and he said something similar which was related from the Prophet, may Allah bless him and grant him peace."  

عَنْ صَفْوَانَ بْنِ عَبْدِ اللهِ بْنِ صَفْوَانَ وَكَانَتْ تَحْتَهُ الدَّرْدَاءُ بِنْتُ أَبِي الدَّرْدَاءِ قَالَ قَدِمْتُ عَلَيْهِمُ الشَّامَ فَوَجَدْتُ أُمَّ الدَّرْدَاءِ فِي الْبَيْتِ وَلَمْ أَجِدْ أَبَا الدَّرْدَاءِ قَالَتْ أَتُرِيدُ الْحَجَّ الْعَامَ؟ قُلْتُ نَعَمْ قَالَتْ فَادْعُ اللَّهَ لَنَا بِخَيْرٍ فَإِنَّ النَّبِيَّ ﷺ كَانَ يَقُولُ إِنَّ دَعْوَةَ الْمَرْءِ الْمُسْلِمِ مُسْتَجَابَةٌ لأَخِيهِ بِظَهْرِ الْغَيْبِ عِنْدَ رَأْسِهِ مَلَكٌ مُوَكَّلٌ كُلَّمَا دَعَا لأَخِيهِ بِخَيْرٍ قَالَ آمِينَ وَلَكَ بِمِثْلٍ قَالَ فَلَقِيتُ أَبَا الدَّرْدَاءِ فِي السُّوقِ فَقَالَ مِثْلَ ذَلِكَ يَأْثُرُ عَنِ النَّبِيِّ ﷺ  

'Abdullah ibn 'Amr reported that a man said, "O Allah, forgive me and Muhammad alone!" The Prophet, may Allah bless him and grant him peace, said, "You have veiled it from many people."  

قَالَ رَجُلٌ اللَّهُمَّ اغْفِرْ لِي وَلِمُحَمَّدٍ وَحْدَنَا فَقَالَ النَّبِيُّ ﷺ لَقَدْ حَجَبْتَهَا عَنْ نَاسٍ كَثِيرٍ  

Ibn 'Umar said, "I heard the Prophet, may Allah bless him and grant him peace, asking Allah to forgive him a hundred times in this assembly with the words, 'O Allah, forgive me and turn to me and show mercy to me. You are the Ever-Turning back (to his slaves), Merciful.'"  

سَمِعْتُ النَّبِيَّ ﷺ يَسْتَغْفِرُ اللَّهَ فِي الْمَجْلِسِ مِئَةَ مَرَّةٍ رَبِّ اغْفِرْ لِي وَتُبْ عَلَيَّ وَارْحَمْنِي إِنَّكَ أَنْتَ التَّوَّابُ الرَّحِيمُ