Musnad Ahmad 31:606

Abdullah ibn al-Walid narrated to us, Sufyan narrated to us, from Salamah ibn Kuhayl, from Qaza'ah, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no wisal (continuous fasting without breaking it)," meaning in fasting.