I came while the Prophet ﷺ was saying the prayer. I sat down and did not pray along with them. The Messenger of Allah ﷺ turned towards us and saw that Yazid was sitting there. He said: Did you not embrace Islam, Yazid? He replied: Why not, Messenger of Allah; I have embraced Islam. He said: What prevented you from saying prayer along with the people? He replied: I have already prayed in my house, and I thought that you had prayed (in congregation). He said: When you come to pray (in the mosque) and find the people praying, then you should pray along with them, though you have already prayed. This will be a supererogatory prayer for you and that will be counted as obligatory.  

جِئْتُ وَالنَّبِيُّ ﷺ فِي الصَّلاَةِ فَجَلَسْتُ وَلَمْ أَدْخُلْ مَعَهُمْ فِي الصَّلاَةِ قَالَ فَانْصَرَفَ عَلَيْنَا رَسُولُ اللَّهِ ﷺ فَرَأَى يَزِيدَ جَالِسًا فَقَالَ أَلَمْ تُسْلِمْ يَا يَزِيدُ قَالَ بَلَى يَا رَسُولَ اللَّهِ قَدْ أَسْلَمْتُ قَالَ فَمَا مَنَعَكَ أَنْ تَدْخُلَ مَعَ النَّاسِ فِي صَلاَتِهِمْ قَالَ إِنِّي كُنْتُ قَدْ صَلَّيْتُ فِي مَنْزِلِي وَأَنَا أَحْسِبُ أَنْ قَدْ صَلَّيْتُمْ فَقَالَ إِذَا جِئْتَ إِلَى الصَّلاَةِ فَوَجَدْتَ النَّاسَ فَصَلِّ مَعَهُمْ وَإِنْ كُنْتَ قَدْ صَلَّيْتَ تَكُنْ لَكَ نَافِلَةً وَهَذِهِ مَكْتُوبَةً  

[Machine] Sa'id ibn al-Sa'ib al-Ta'ifi narrated from Nuha ibn Sa'sa'a who narrated from Yazid ibn 'Amir, he said: I came to the Prophet ﷺ during either the Dhuhr or Asr prayer, and I had already performed them at home. When I found the Prophet ﷺ praying, I sat down and did not join him in the prayer. The Messenger of Allah ﷺ finished his prayer and saw me sitting, so he said, "Did you not offer the greetings, O Yazid?" I said, "Yes, O Messenger of Allah, I did greet (the prayer)." He said, "What prevents you from joining the people in their prayer?" I said, "I had already prayed at home and I thought that you had already prayed." He said, "When you come to the prayer and find the people praying, then pray with them. Even if you have already prayed, it will be a voluntary prayer for you. And this is prescribed."  

ثَنَا سَعِيدُ بْنُ السَّائِبِ الطَّائِفِيُّ عَنْ نُوحِ بْنِ صَعْصَعَةَ عَنْ يَزِيدَ بْنِ عَامِرٍ قَالَ جِئْتُ وَالنَّبِيُّ ﷺ فِي الصَّلَاةِ إِمَّا فِي الظُّهْرِ وإِمَّا فِي الْعَصْرِ وَكُنْتُ صَلَّيْتُهُمَا فِي الْمَنْزِلِ فَلَمَّا وَجَدْتُ النَّبِيَّ ﷺ فِي الصَّلَاةِ جَلَسْتُ وَلَمْ أدْخُلْ مَعَهُمْ فِي الصَّلَاةِ فَانْصَرَفَ عَلَيْنَا رَسُولُ اللهِ ﷺ فَرَآنِي جَالِسًا فَقَالَ أَلَمْ تُسْلِمْ يَا يَزِيدُ قُلْتُ بَلَى يَا رَسُولَ اللهِ قَد أَسْلَمْتُ فَقَالَ مَا يَمْنَعُكُ أَنْ تَدْخُلَ مَعَ النَّاسِ فِي صَلَاتِهِمْ قُلْتُ إِنِّي كُنْتُ صَلَّيْتُ فِي مَنْزِلِي وَأَنَا أَحْسِبُ أَنْ قَد صَلَّيْتُمْ قَالَ فَإِذَا جِئْتَ الصَّلَاةَ فَوَجَدْتَ النَّاسَ يُصَلُّونَ فَصَلِّ مَعَهُمْ وَإِنْ كُنْتَ قَد صَلَّيْتَ تَكُونُ لَكَ نَافِلَةً وَهَذِه مَكْتُوبَةٌ  

I came while the Prophet ﷺ was saying the prayer. I sat down and did not pray along with them. The Messenger of Allah ﷺ turned towards us and saw that Yazid was sitting there. He said: Did you not embrace Islam, Yazid? He replied: Why not, Messenger of Allah; I have embraced Islam. He said: What prevented you from saying prayer along with the people? He replied: I have already prayed in my house, and I thought that you had prayed (in congregation). He said: When you come to pray (in the mosque) and find the people praying, then you should pray along with them, though you have already prayed. This will be a supererogatory prayer for you and that will be counted as obligatory. (Using translation from Abū Dāʾūd 577)   

جِئْتُ وَالنَّبِيُّ ﷺ فِي الصَّلَاةِ فَجَلَسْتُ وَلَمْ أَدْخُلْ مَعَهُمْ فِي الصَّلَاةِ قَالَ فَانْصَرَفَ عَلَيْنَا بِوَجْهِهِ رَسُولُ اللهِ ﷺ فَرَأَى يَزِيدَ جَالِسًا فَقَالَ أَلَمْ تُسْلِمْ يَا يَزِيدُ؟ قَالَ بَلَى يَا رَسُولَ اللهِ قَدْ أَسْلَمْتُ قَالَ وَمَا مَنَعَكَ أَنْ تَدْخُلَ مَعَ النَّاسِ فِي صَلَاتِهِمْ؟ قَالَ إِنِّي كُنْتُ صَلَّيْتُ فِي مَنْزِلِي وَأَنَا أَحْسَبُ أَنْ قَدْ صَلَّيْتُمْ فَقَالَ إِذَا جِئْتَ إِلَى الصَّلَاةِ فَوَجَدْتَ النَّاسَ فَصَلِّ مَعَهُمْ وَإِنْ كُنْتَ قَدْ صَلَّيْتَ فَلْتَكُنْ لَكَ نَافِلَةً وَهَذِهِ مَكْتُوبَةٌ فَهَذَا مُوَافِقٌ لِمَا مَضَى فِي إِعَادَةِ الصَّلَاةِ فِي الْجَمَاعَةِ مُخَالِفٌ لَهُ فِي الْمَكْتُوبَةِ مِنْهُمَا وَمَا مَضَى أَكْثَرُ وَأَشْهُرُ فَهُوَ أَوْلَى وَاللهُ أَعْلَمُ