It is narrated from Aisha (may Allah be pleased with her) that she said: "It was revealed in the Qur'an that ten times suckling makes (marriage) unlawful, then it was abrogated and five times suckling became the cause of prohibition, and only those who had completed five sucklings would come to Aisha (may Allah be pleased with her)."
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1179
Hadith Takhrijاخرجه مسلم الرضاع، باب التحريم بخمس رضعات (1452)۔