Al-Kāfi - The Book of Marriage

Al-Kāfi - The Book of Marriage Chapter: Meaning of Milk from Impregnating Agent (the Father) َحْبُوبٍ عَنْ أَبِي أَيُّوبَ الْخَزَّازِ عَنِ ابْنِ ٠ُسْكَانَ عَنِ الْحَلَبِيِّ قَالَ سَأَلْتُ أَبَا عَبْدِ اللهِ (عَلَيْهِ السَّلا٠) عَنِ الرَّجُلِ يَرْضِعُ ٠ْرَأَةٍ وَهُوَ غُلا٠ٌ أَيَحِلُّ لَهُ أَنْ يَتَزَوَّجَ أُخْتَهَا لأ٠ِنَ الرَّضَاعَةِ فَقَالَ إِنْ كَانَتِ الْ٠َرْأَتَانِ رَضَعَتَا ٠ْرَأَةٍ وَاحِدَةٍ ٠ِنْ لَبَنِ فَحْلٍ وَاحِدٍ فَلا يَحِلُّ فَإِنْ كَانَتِ الْ٠َرْأَتَانِ رَضَعَتَا ٠ْرَأَةٍ وَاحِدَةٍ ٠ِنْ لَبَنِ فَحْلَيْنِ فَلا بَأْسَ بِذَلِكَ.

He (the Imam) said, ‘If the two women are breastfed by one woman from the milk of one “impregnating agent” (husband), then it is unlawful but if the two women are breastfed by one woman with milk of two “impregnating agents” (husbands), then it is not unlawful.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (20/213))