"There is no blame upon them concerning their fathers" up to His saying: "nor their women," meaning: the Muslim women, "nor what their right hands possess." Likewise, foster relationships (al-rada') are in the same category as what has been mentioned of those who may enter upon the wives of the Prophet while in the veil.
Surat al-Ahzab (Verse 56).
﴿لَا جُنَاحَ عَلَيْهِنَّ فِي آبَائِهِنَّ﴾ إِلَى قَوْله: ﴿وَلَا نسائهن﴾ يَعْنِي: الْمُسْلِمَاتُ ﴿وَلا مَا مَلَكَتْ أيمانهن﴾ وَكَذَلِكَ الرَّضَاعُ بِمَنْزِلَةِ الَّذِي ذُكِرَ مِمَّنْ يَدْخُلُ عَلَى أَزْوَاجِ النَّبِيِّ فِي الْحجاب.
سُورَة الْأَحْزَاب (آيَة ٥٦).