Masruq (may Allah have mercy on him) said concerning the saying of Allah: "And the mothers of your wives" [Surah al-Nisa: 23]: What Allah has left (unqualified), you also leave it (so), and what He has made clear, follow it. Then he recited: "And your stepdaughters who are raised under your guardianship, born of your wives with whom you have had intercourse; but if you have not had intercourse with them, there is no sin upon you." [Surah al-Nisa: 23] He left this (unqualified) and made that clear.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13909