Musnad Ahmad 31:916

'Affan narrated to us, Hammad ibn Salamah narrated to us, Bishr ibn Harb informed us, from Abu Sa'id al-Khudri, that the Messenger of Allah (peace and blessings of Allah be upon him) forbade *wisal* (continuous fasting without breaking it) in fasting. His companions did not cease [asking] him until he granted them a concession from the *suhur* (pre-dawn meal) to the *suhur*.