Shu'bah narrated to us from Amr bin Dinar that he (that is, Amr bin Dinar) heard a man say to Abdullah bin Umar (may Allah be pleased with them both): The Commander of the Believers, Abdullah bin al-Zubayr (may Allah be pleased with them both), says that one or two sucklings do not establish the prohibition. Abdullah bin Umar (may Allah be pleased with them both) said: The Book of Allah is more truthful than the Commander of the Believers. Then he recited: "Forbidden to you are your mothers, your daughters and your sisters" until he reached: "and your mothers who suckled you and your sisters through suckling" [Surah al-Nisa: 23].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15643