Hadith 10:99
Ibn ‘Abbas said:
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.
عَنِ ابْنِ عَبَّاسٍ قَالَ: حُرِّمَ مِنَ النَّسَبِ سَبْعٌ وَمِنَ الصِّهْرِ سَبْعٌ ثُمَّ قَرَأَ: (حُرِّمَتْ عَلَيْكُم أُمَّهَاتكُم) الْآيَة. رَوَاهُ البُخَارِيّ
Original Reference: Mishkat al-Masabih 3181