It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "One or two sucks do not establish the prohibition."
Muslim narrated it in his Sahih from Zuhayr bin Harb and others, from Isma'il bin Ibrahim Ibn Ulayyah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15625