Musannaf Ibn Abi Shayba 3:5563

Hussain bin Ali narrated to us, from Abu Harzah, a sheikh from the people of Medina—and he praised him well—from Al-Qasim bin Muhammad, who said: Some of the nephews of Aisha entered upon her, then he stood up to go to the mosque. She said to him: "Sit down, for I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'None of you should pray while food is present, nor while he is suppressing the two impurities.'"