Musnad Ahmad 1159:27

Ya'qub narrated to us, he said: My father narrated to us, he said: And Ibn Ishaq narrated to us, he said: Muhammad ibn Muslim ibn Shihab narrated to me, from Abu Salamah ibn 'Abd al-Rahman ibn 'Awf, from Abu Sufyan ibn Sa'id ibn al-Akhnas ibn Shariq, who said: I entered upon Umm Habibah, and she was his maternal aunt, and she gave me a drink of *sawiq* (roasted barley flour). When I stood up, she said to me: "O my son, do not pray until you perform ablution, for the Messenger of Allah, peace and blessings of Allah be upon him, has commanded us to perform ablution from food that fire has touched."