Becoming Mahram is established by Five Breastfeedings
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ، عَنْ عَمْرَةَ، عَنْ عَائِشَةَ، أَنَّهَا قَالَتْ كَانَ فِيمَا أُنْزِلَ مِنَ الْقُرْآنِ عَشْرُ رَضَعَاتٍ مَعْلُومَاتٍ يُحَرِّمْنَ . ثُمَّ نُسِخْنَ بِخَمْسٍ مَعْلُومَاتٍ فَتُوُفِّيَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَهُنَّ فِيمَا يُقْرَأُ مِنَ الْقُرْآنِ .
'A'isha (Allah be pleased with, her) reported that it had been revealed in the Holy Qur'an that ten clear sucklings make the marriage unlawful, then it was abrogated (and substituted) by five sucklings and Allah's Messenger (ﷺ) died and it was before that time (found) in the Holy Qur'an (and recited by the Muslims).