Sayyiduna Imran bin Husayn (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said to him, or said to a man while he was listening: "Did you fast any day at the end of this month?" The man said: No, O Messenger of Allah. He (peace and blessings be upon him) said: "When you have broken your fast, then keep two fasts in its place."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7967