Musnad Ahmad 1280:2

Hushaym narrated to us, Mansur—meaning Ibn Zadhan—narrated to us, from Khubayb ibn Abd al-Rahman, from his paternal aunt, Anisah bint Khubayb, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When Ibn Umm Maktum gives the adhan, eat and drink; and when Bilal gives the adhan, do not eat and do not drink." She said: "And a woman would have some of her suhur remaining, so she would say to Bilal: 'Wait until I finish my suhur.'"