Musnad Ahmad 30:2951

'Abd al-Rahman narrated to us, Sufyan narrated to us, from Habib, who said: Ibn al-Mutawwas 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 in Ramadan without an illness or a concession, the fasting of the entire lifetime will not compensate for it, even if he were to fast it." Sufyan said: Habib said: 'Umarah narrated to me, from Abu al-Mutawwas. So I met Abu al-Mutawwas, and he narrated it to me. Abu Nu'aym narrated it to us, and Abu al-Mutawwas said: