Abu Wa'il narrates from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) concerning a woman who is given three divorces before consummation: "She is not lawful for him until she marries another husband."
Al-Thawri narrated it through Asim from Zirr, and Zirr from Sayyiduna Ibn Mas'ud (may Allah be pleased with him), thus: He said: "When someone gives three divorces before consummation, he used to regard her as being like a woman with whom the marriage had been consummated."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9586