Musnad Ahmad 1153:615

Bahz narrated to us, he said: Shu'bah narrated to us, he said: Ash'ath ibn Sulaym narrated to us, that he heard his father narrating from Masruq, from 'Aishah, that the Messenger of Allah (peace and blessings of Allah be upon him) entered upon her while a man was with her. He said: The face of the Messenger of Allah (peace and blessings of Allah be upon him) changed, as if it was difficult for him. She said: "O Messenger of Allah, [he is] my brother." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Look into who your brothers are, for indeed, suckling is only from hunger."