Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) "ordered the one who had broken a fast in Ramadan to make up one fast."
Abd al-Jabbar bin Umar al-Ayli also narrated it from al-Zuhri, and he is not strong.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8056