Sayyiduna Abu Huraira (may Allah be pleased with him) narrated from the Messenger of Allah (peace and blessings be upon him), he (peace be upon him) said: "Whoever leaves one fast of Ramadan without a concession given by Allah, then even if he fasts for his entire life, it will not make up for it."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الصوم / 407