Allah said,

﴿وَحَلَـئِلُ أَبْنَآئِكُمُ الَّذِينَ مِنْ أَصْلَـبِكُمْ﴾

(The wives of your sons who (spring) from your own loins,) Therefore, you are prohibited to marry the wives of your own sons, but not the wives of your adopted sons, as adoption was common practice in Jahiliyyah. Allah said,

﴿فَلَمَّا قَضَى زَيْدٌ مِّنْهَا وَطَراً زَوَّجْنَـكَهَا لِكَىْ لاَ يَكُونَ عَلَى الْمُؤْمِنِينَ حَرَجٌ فِى أَزْوَاجِ أَدْعِيَآئِهِمْ﴾

(So when Zayd had accomplished his desire from her (i.e. divorced her), We gave her to you in marriage, so that (in future) there may be no difficulty to the believers in respect of (the marriage of) the wives of their adopted sons when the latter have no desire to keep them (i.e. they had divorced them).) ﴿33:37﴾ Ibn Jurayj said, "I asked `Ata' about Allah's statement,

﴿وَحَلَـئِلُ أَبْنَآئِكُمُ الَّذِينَ مِنْ أَصْلَـبِكُمْ﴾

(The wives of your sons who (spring) from your own loins,) He said, `We were told that when the Prophet married the ex-wife of Zayd (who was the Prophet's adopted son before Islam prohibited this practice), the idolators in Makkah criticized him. Allah sent down the Ayat:

﴿وَحَلَـئِلُ أَبْنَآئِكُمُ الَّذِينَ مِنْ أَصْلَـبِكُمْ﴾

(The wives of your sons who (spring) from your own loins),

﴿وَمَا جَعَلَ أَدْعِيَآءَكُمْ أَبْنَآءَكُمْ﴾

(nor has He made your adopted sons your real sons.) ﴿33:4﴾, and,

﴿مَّا كَانَ مُحَمَّدٌ أَبَآ أَحَدٍ مّن رِّجَالِكُمْ﴾

(Muhammad is not the father of any of your men) ﴿33:40﴾.''' Ibn Abi Hatim recorded that Al-Hasan bin Muhammad said, "These Ayat are encompassing,

﴿وَحَلَـئِلُ أَبْنَآئِكُمُ﴾

(the wives of your sons), and,

﴿وَأُمَّهَـتُ نِسَآئِكُمْ﴾

(your wives' mothers). This is also the explanation of Tawus, Ibrahim, Az-Zuhri and Makhul. It means that these two Ayat encompass these types of women, whether the marriage was consummated or not, and there is a consensus on this ruling.