Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
bayhaqi:12506Abū Saʿīd b. Abū ʿAmr > Abū al-ʿAbbās al-Aṣam > al-Rabīʿ > al-Shāfiʿī

[Machine] "And we said: When the Magian man converts to Islam and his wife, daughter, or sister becomes his wife, we look into the two greatest lineages and we pass it down to him. And we discard the other lineage. The greater of the two we establish in all cases. So if she is a mother or a sister, we pass it down as a mother, because a mother is established in all cases, while a sister can be removed. And so it is with all their obligations in these situations. And some people say we pass it down from both sides together."  

البيهقي:١٢٥٠٦أَخْبَرَنَا أَبُو سَعِيدِ بْنُ أَبِي عَمْرٍو ثنا أَبُو الْعَبَّاسِ الْأَصَمُّ أنا الرَّبِيعُ أنا الشَّافِعِيُّ قَالَ

وَقُلْنَا إِذَا أَسْلَمَ الْمَجُوسِيُّ وَابْنَةُ الرَّجُلِ امْرَأَتُهُ أَوْ أُخْتُهُ أُمُّهُ نَظَرْنَا إِلَى أَعْظَمِ النَّسَبَيْنِ فَوَرَّثْنَاهَا بِهِ وَأَلْقَيْنَا الْأُخْرَى وَأَعْظَمُهُمَا أَثْبَتُهُمَا بِكُلِّ حَالٍ فَإِذَا كَانَتْ أُمًّا أُخْتًا وَرَّثْنَاهَا بِأَنَّهَا أُمٌّ وَذَلِكَ أَنَّ الْأُمَّ قَدْ ثَبَتَتْ فِي كُلِّ حَالٍ وَالْأُخْتَ قَدْ تَزُولُ وَهَكَذَا جَمِيعُ فَرَائِضِهِمْ عَلَى هَذِهِ الْمَنَازِلِ وَقَالَ بَعْضُ النَّاسِ أُوَرِّثُهَا مِنَ الْوَجْهَيْنِ مَعًا