The Prophet ﷺ sent for the Ansar (and when they came), he asked, 'Is there any stranger amongst you?" They said, "No except the son of our sister." Messenger of Allah ﷺ said, "The son of the sister of some people belongs to them."  

دَعَا النَّبِيُّ ﷺ الأَنْصَارَ فَقَالَ هَلْ فِيكُمْ أَحَدٌ مِنْ غَيْرِكُمْ قَالُوا لاَ إِلاَّ ابْنُ أُخْتٍ لَنَا فَقَالَ رَسُولُ اللَّهِ ﷺ ابْنُ أُخْتِ الْقَوْمِ مِنْهُمْ