He (the Holy Prophet) sent me along with Abu 'Amir and Abu 'Amir received a wound in his knee from the arrow, (shot by) a person of Bani Jusham. It stuck in his knee. I went to him and said: Uncle, who shot an arrow upon you? Abu 'Amir pointed out to Abu Musa and said: Verily that one who shot an arrow upon me in fact killed me. Abu Musa said: I followed him with the determination to kill him and overtook him and when he saw me he turned upon his heels. I followed him and I said to him: Don't you feel ashamed (that you run), aren't you an Arab? Why don't you stop? He stopped and I had an encounter with him and we exchanged the strokes of (swords). I struck him with the sword and killed him. Then I came back to Abu Amir and said: Verily Allah has killed the one who killed you. And he said: Now draw out this arrow. I drew out the arrow and there came out from that (wound) water. Abu 'Amir said: My nephew, go to Messenger of Allah ﷺ and convey my greetings to him and tell him that Abu Amir begs you to ask forgiveness for him. And Abu Amir appointed me as the chief of the people and he died after a short time. When I came to Allah's Apostle ﷺ I visited him and he had been lying on the cot woven by strings and there was (no) bed over it and so there had been marks of the strings on the back of Messenger of Allah ﷺ and on his sides. I narrated to him what had happened to us and narrated to him about Abu Amir and said to him that he had made a request to the effect that forgiveness should be sought for him (from Allah). Thereupon Messenger of Allah (may peace be. upon him) called for water and performed ablution with it. He then lifted his hands and said. O Allah, grant pardon to Thy servant Abu Amir. (The Prophet had raised his hands so high for supplication) that I saw the whiteness of his armpits. He again said: O Allah, grant him distinction amongst the majority of Thine created beings or from amongst the people. I said: Messenger of Allah, ask forgiveness for me too. Thereupon Allah's Apostle ﷺ said: Allah, forgive the sins of Abdullah b. Qais (Abu Musa Ash'ari) and admit him to an elevated place on the Day of Resurrection. Abu Burda said: One prayer is for abu 'Amir and the other is tor Abu Musa. (Using translation from Muslim 2498)  

لَمَّا جَاءَ النَّبِيُّ ﷺ مِنْ حُنَيْنٍ بَعَثَ أَبَا عَامِرٍ عَلَى جَيْشٍ إِلَى أَوْطَاسٍ فَلَقِيَ ابْنَ الصِّمَّةِ فَقُتِلَ وَهَزَمَ اللهُ أَصْحَابَهُ قَالَ أَبُو مُوسَى فَرُمِيَ أَبُو عَامِرٍ فِي رُكْبَتِهِ رَمَاهُ رَجُلٌ مِنْ بَنِي جُشَمٍ بِسَهْمٍ فَأَثْبَتَهُ فِي رُكْبَتِهِ فَانْتَهَيْتُ إِلَيْهِ فَقُلْتُ يَا عَمُّ «مَنْ رَمَاكَ؟ فَأَشَارَ أَبُو عَامِرٍ إِلَى أَبِي مُوسَى» فَقَالَ «إِنَّ ذَاكَ قَاتِلِي تَرَاهُ ذَلِكَ الَّذِي رَمَانِي» قَالَ أَبُو مُوسَى «فَقَصَدْتُ إِلَيْهِ فَاعْتَمَدْتُهُ فَلَحِقْتُهُ فَلَمَّا رَآنِي وَلَّى عَنَى ذَاهِبًا فَاتَّبَعْتُهُ» وَجَعَلْتُ أَقُولُ لَهُ «أَلَا تَسْتَحْيِ؟ أَلَسْتَ عَرَبِيًّا؟ أَلَا تَثْبُتُ؟ فَكَرَّ فَالْتَقَيْتُ أَنَا وَهُوَ فَاخْتَلَفْنَا ضَرْبَتَيْنِ فَضَرَبْتُهُ بِالسَّيْفِ فَقَتَلْتُهُ ثُمَّ رَجَعْتُ إِلَى أَبِي عَامِرٍ» فَقُلْتُ قَدْ قَتَلَ اللهُ صَاحِبَكَ قَالَ «فَانْزِعْ هَذَا السَّهْمَ فَنَزَعْتُهُ فَنَزَا مِنْهُ الْمَاءُ» فَقَالَ يَا ابْنَ أَخِي انْطَلِقْ إِلَى رَسُولِ اللهِ ﷺ فَأَقْرِئْهُ مِنِّي السَّلَامَ وَقُلْ لَهُ إِنَّهُ يَقُولَ لَكَ «اسْتَغْفِرْ لِي» قَالَ وَاسْتَخْلَفَنِي أَبُو عَامِرٍ عَلَى النَّاسِ فَمَكَثَ يَسِيرًا ثُمَّ إِنَّهُ مَاتَ فَلَمَّا رَجَعْتُ إِلَى رَسُولِ اللهِ ﷺ دَخَلْتُ عَلَيْهِ وَهُوَ فِي بَيْتٍ عَلَى سَرِيرٍ مُرَمَّلٍ وَعَلَيْهِ فِرَاشٌ وَقَدْ أَثَّرَ رِمَالُ السَّرِيرِ بِظَهْرِ رَسُولِ اللهِ ﷺ وَجَنْبَيْهِ فَأَخْبَرْتُهُ بِخَبَرِنَا وَخَبَرِ أَبِي عَامِرٍ فَقُلْتُ قَالَ لِي «قُلْ لَهُ اسْتَغْفِرْ لِي فَدَعَا رَسُولُ اللهِ ﷺ بِمَاءٍ فَتَوَضَّأَ ثُمَّ رَفَعَ يَدَيْهِ» فَقَالَ اللهُمَّ اغْفِرْ لِعُبْيدٍ أَبِي عَامِرٍ حَتَّى رَأَيْتُ بَيَاضَ إِبْطَيْهِ ثُمَّ قَالَ «اللهُمَّ اجْعَلْهُ يَوْمَ الْقِيَامَةِ فَوْقَ كَثِيرٍ مِنْ خَلْقِكَ أَوْ مِنَ النَّاسِ» فَقُلْتُ وَلِي يَا رَسُولَ اللهِ فَاسْتَغْفِرْ فَقَالَ النَّبِيُّ ﷺ «اللهُمَّ اغْفِرْ لِعَبْدِ اللهِ بْنِ قَيْسٍ ذَنْبَهُ وَأَدْخِلْهُ يَوْمَ الْقِيَامَةِ مُدْخَلًا كَرِيمًا» قَالَ أَبُو بُرْدَةَ إِحْدَاهُمَا لِأَبِي عَامِرٍ وَالْأُخْرَى لِأَبِي مُوسَى