Musnad Ahmad 1153:1794

Isma'il narrated to us, he said: Ayyub informed us, from 'Abdullah ibn Abi Mulaykah, from 'Abdullah ibn al-Zubayr, from 'Aishah, that the Prophet, peace and blessings of Allah be upon him, said: "One suckling does not make [marriage] unlawful, nor do two sucklings."