Musnad Ahmad 30:2950

Yahya ibn Sa'id narrated to us, from Sufyan, who said: Habib narrated to me, from 'Umarah, from Ibn al-Mutawwas. I met Ibn al-Mutawwas, and he narrated to me from his father, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever breaks his fast for one day of Ramadan without a concession that Allah has granted him, the fasting of an entire lifetime will not make up for it, even if he were to fast it."