Sahih Muslim 1452
Sahih Muslim · Book 17: The Book of Suckling · Becoming Mahram is established by Five Breastfeedings
وَحَدَّثَنَاهُ مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا عَبْدُ الْوَهَّابِ ، قَالَ سَمِعْتُ يَحْيَى بْنَ سَعِيدٍ ، قَالَ أَخْبَرَتْنِي عَمْرَةُ ، أَنَّهَا سَمِعَتْ عَائِشَةَ ، تَقُولُ . بِمِثْلِهِ .
Ahadith like this is transmitted by 'A'isha through another chain of narrators.