Tafsir Ibn Kathir -> Surah An-Nisa -> A Doubt and Rebuttal

Why is the wife of one's son from suckling prohibited for him for marriage - that is, if she is no longer married to his son from suckling - as the majority of scholars state, although they are not related by blood The answer is the Prophet's statement,

«يَحْرُمُ مِنَ الرَّضَاعِ مَا يَحْرُمُ مِنَ النَّسَب»

(Suckling prohibits what blood relations prohibit.)