كتاب الرضاع
17
The Book of Suckling
(6)
Chapter: Becoming Mahram is established by Five Breastfeedings
(6)
باب التَّحْرِيمِ بِخَمْسِ رَضَعَاتٍ ‏

'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).
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 ‏.‏
Reference : Sahih Muslim 1452 b
In-book reference : Book 17, Hadith 31
USC-MSA web (English) reference : Book 8, Hadith 3422
  (deprecated numbering scheme)