Ikrimah (may Allah have mercy on him) narrates from Abdullah bin Abbas (may Allah be pleased with them both) concerning a man who committed zina with his wife's mother; he said: He has transgressed two sanctities, but his wife does not become unlawful to him.
Al-Zuhri narrated from Ali (may Allah be pleased with him) the like of our view, and it is mursal (its chain is broken); it is also the view of Ibn al-Musayyib, Urwah and al-Zuhri.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13962