Mishkat al-Masabih 30 Fine Qualities كتاب المناقب 212

وَعَنْ أَبِي مُوسَى الْأَشْعَرِيِّ قَالَ: قَدِمْتُ أَنَا وَأَخِي مِنَ الْيَمَنِ فَمَكَثْنَا حِينًا مَا نَرَى إِلَّا أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ رَجُلٌ مِنْ أَهْلِ بَيْتِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لِمَا نُرَى مِنْ دُخُولِهِ وَدُخُولِ أُمِّهِ عَلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ. مُتَّفَقٌ عَلَيْهِ

Abu Musa al-Ash`ari said: My brother and I came from the Yemen and for quite a time we had no idea that `Abdallah b. Mas’ud was other than a member of the Prophet’s family because of seeing how frequently he and his mother went in to visit the Prophet. (Bukhari and Muslim.)