Sahih al-Bukhari 3528
Book 61: Virtues and Merits of the Prophet (pbuh) and his Companions · Narrated by Anas
Arabic
حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ دَعَا النَّبِيُّ صلى الله عليه وسلم الأَنْصَارَ فَقَالَ " هَلْ فِيكُمْ أَحَدٌ مِنْ غَيْرِكُمْ ". قَالُوا لاَ، إِلاَّ ابْنُ أُخْتٍ لَنَا. فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " ابْنُ أُخْتِ الْقَوْمِ مِنْهُمْ ".
English translation
Narrated Anas: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." Allah's Messenger (ﷺ) said, "The son of the sister of some people belongs to them
Reference: Sahih al-Bukhari 3528, Book of Virtues and Merits of the Prophet (pbuh) and his Companions. English translation by Dr. Muhammad Muhsin Khan.