It is narrated from Hanzalah bin Abi Sufyan (may Allah have mercy on him) that Salim (may Allah have mercy on him) was asked whether a single suckling establishes the prohibition. He said: Zayd bin Thabit (may Allah be pleased with him) narrated to us "that one suckling, two sucklings and three sucklings do not make (marriage) unlawful."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15637