Musannaf Ibn Abi Shayba 9:1121

Waki’ narrated to us, from Sufyan, from Ash’ath ibn Abi al-Sha’tha’, from his father, from Masruq, from ‘Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, suckling is only [that which occurs] from hunger."