Becoming Mahram is established by Five Breastfeedings
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ الْقَعْنَبِيُّ، حَدَّثَنَا سُلَيْمَانُ بْنُ بِلاَلٍ، عَنْ يَحْيَى، - وَهُوَ ابْنُ سَعِيدٍ - عَنْ عَمْرَةَ، أَنَّهَا سَمِعَتْ عَائِشَةَ، تَقُولُ - وَهْىَ تَذْكُرُ الَّذِي يُحَرِّمُ مِنَ الرَّضَاعَةِ - قَالَتْ عَمْرَةُ فَقَالَتْ عَائِشَةُ نَزَلَ فِي الْقُرْآنِ عَشْرُ رَضَعَاتٍ مَعْلُومَاتٍ ثُمَّ نَزَلَ أَيْضًا خَمْسٌ مَعْلُومَاتٌ .
'Amra reported that she heard 'A'isha (Allah he pleased with her) discussing fosterage which (makes marriage) unlawful; and she ('A'isha) said: There was revealed in the Holy Qur'an ten clear sucklings, and then five clear (sucklings).