Mishkat al-Masabih 12 Inheritance and Wills كتاب الفرائض والوصايا 5

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «ابْنُ أُخْتِ الْقَوْمِ مِنْهُم».

He reported God’s Messenger as saying, “A sister’s son has blood- relationship to her family.” (Bukhari and Muslim.)