It is narrated from Aishah (may Allah be pleased with her): "The verse of ten known sucklings was revealed in the Qur'an, then afterwards it was abandoned in favour of five," or she said: "five known sucklings." Muslim narrated it in his Sahih from Muhammad bin al-Muthanna.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15620