It is narrated from Amr bin Dinar (may Allah have mercy on him) that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) was asked about something concerning suckling. He (may Allah be pleased with them both) said: I know nothing except that Allah Almighty has made the foster sister, that is, the milk sister, unlawful. I said: The Commander of the Believers, Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both), says that neither one suckling nor two sucklings, nor one suck nor two sucks, establish the prohibition. Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: The decree of Allah is better than your decree and the decree of the Commander of the Believers along with you.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15642