It is narrated from Ubaydullah bin Abdullah bin Utbah (may Allah have mercy on him) that Abdullah bin Abbas (may Allah be pleased with them both) used to say that suckling, whether little or much, establishes the prohibition in the cradle. Ibn Shihab (may Allah have mercy on him) said that there is no suckling after two complete years. This is how it is narrated from Ibn Abbas (may Allah be pleased with them both) in this report.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15645