عَنِ ابْنِ عَبَّاسٍ قَالَ: حُرِّمَ مِنَ النَّسَبِ سَبْعٌ وَمِنَ الصِّهْرِ سَبْعٌ ثُمَّ قَرَأَ: (حُرِّمَتْ عَلَيْكُم أُمَّهَاتكُم) الْآيَة. رَوَاهُ البُخَارِيّ

Seven classes of women are prohibited by reason of consanguinity and seven by reason of relationship by marriage. He then recited, "Prohibited to you are your mothers ...” (Al-Qur’an 4:23). Bukhari transmitted it.