بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1096
Marriage
وَعَنِ أَنَسٍ, أَنَّ اَلنَّبِيَّ - صلى الله عليه وسلم -قَالَ: { أَبْصِرُوهَا, فَإِنْ جَاءَتْ بِهِ أَبْيَضَ سَبِطًا فَهُوَ لِزَوْجِهَا, وَإِنْ جَاءَتْ بِهِ أَكْحَلَ جَعْدًا, فَهُوَ اَلَّذِي رَمَاهَا بِهِ } مُتَّفَقٌ عَلَيْه ِ [1]
Narrated Anas (RA): The Prophet (ﷺ) said: "Observe her, and if she gives birth to a child which is white complexioned with dark hair, her husband would be its father. But if she gives birth to a child with eyes looking as if they have antimony (Kuhl) in them and curled hair, the man whom her husband charged her with committing adultery is its father." [Agreed upon].
Sunnah.com reference: Book 8, Hadith 153