Sahih Muslim
Sahih Muslim 1452 c
Becoming Mahram is established by Five Breastfeedings
Arabic hadith text
وَحَدَّثَنَاهُ مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الْوَهَّابِ، قَالَ سَمِعْتُ يَحْيَى بْنَ سَعِيدٍ، قَالَ أَخْبَرَتْنِي عَمْرَةُ، أَنَّهَا سَمِعَتْ عَائِشَةَ، تَقُولُ . بِمِثْلِهِ
Translation
Ahadith like this is transmitted by 'A'isha through another chain of narrators.