Mishkat al-Masabih 3219
Abu Mas'ud al-Ansari said:
One of the Ansar whose kunya was Abu Shu'aib had a servant who sold meat. He said, “Prepare for me food which will be enough for five; perhaps I shall invite the Prophet along with other four.” He prepared a small meal for him, and then he went and invited him. A man followed them, and the Prophet said, “A man has followed us, Abu Shu'aib, so if you wish you may let him join us, but if you wish you may leave him outside.” He replied, “No, I shall let him join us.” 

(Bukhari and Muslim.)
وَعَنْ أَبِي مَسْعُودٍ الْأَنْصَارِيِّ قَالَ: كَانَ رَجُلٌ مِنَ الْأَنْصَارِ يُكْنَى أَبَا شُعَيْبٍ كَانَ لَهُ غُلَامٌ لَحَّامٌ فَقَالَ: اصْنَعْ لِي طَعَامًا يَكْفِي خَمْسَةً لَعَلِّي أَدْعُو النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ خَامِسَ خَمْسَةٍ فَصَنَعَ لَهُ طعيما ثمَّ أتها فَدَعَاهُ فَتَبِعَهُمْ رَجُلٌ فَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَا أَبَا شُعَيْبٍ إِنَّ رَجُلًا تَبِعَنَا فَإِنْ شِئْتَ أَذِنْتَ لَهُ وَإِنْ شِئْتَ تركته» . قَالَ: لَا بل أَذِنت لَهُ