Al-Kāfi - Volume 5 > Father Marries a Woman and His Son Marries Her Daughter
Hadith #4

4- وَعَنْهُ عَنْ زَيْدِ بْنِ الْجُهَيْمِ الْهِلالِيِّ قَالَ سَأَلْتُ أَبَا عَبْدِ اللهِ (عَلَيْهِ السَّلام) عَنِ الرَّجُلِ يَتَزَوَّجُ الْمَرْأَةَ وَيُزَوِّجُ ابْنَهُ ابْنَتَهَا فَقَالَ إِنْ كَانَتِ الابْنَةُ لَهَا قَبْلَ أَنْ يَتَزَوَّجَ بِهَا فَلا بَأْسَ.

4. It is narrated from the narrator of the previous Hadith from Zayd ibn al-Juhaym al-Hilaliy who has said the following: “This is concerning my question before abu ‘Abd Allah, ‘Alayhi al-Salam, about the case of a man who marries a woman and his son marries the daughter of that woman. He (the Imam) said, ‘If her daughter was there before she married him, it is not unlawful.’”