Mishkat al-Masabih 1154
A man of Asad b. Khuzaima said he put this question to Abu Ayyub al-Ansari:
I* pray at home and then go to the mosque and the time to begin the prayer comes, so I pray along with the congregation, but I feel some uneasiness about that. Abu Ayyub replied, “We asked the Prophet about that and he said that such a person gets a portion of the reward for corporate prayer.” 

* The Arabic has “One of us prays . . . then goes . . .” After that the first person singular is used. While such a construction is quite usual in 'Arabic, it makes impossible English, so I have used the first person all through.

Malik and Abu Dawud transmitted it.
وَعَنْ رَجُلٍ مِنْ أَسَدِ بْنِ خُزَيْمَةَ أَنَّهُ سَأَلَ أَبَا أَيُّوبَ الْأَنْصَارِيَّ قَالَ: يُصَلِّي أَحَدُنَا فِي مَنْزِلِهِ الصَّلَاةَ ثُمَّ يَأْتِي الْمَسْجِدَ وَتُقَامُ الصَّلَاةُ فَأُصَلِّي مَعَهُمْ فَأَجِدُ فِي نَفْسِي شَيْئًا من ذَلِك فَقَالَ أَبُو أَيُّوبَ: سَأَلَنَا عَنْ ذَلِكَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «فَذَلِكَ لَهُ سَهْمُ جَمْعٍ» . رَوَاهُ مَالِكٌ وَأَبُو دَاوُد