A man said that Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "Whoever leaves a day of Ramadan unfasted without any concession will meet Allah in that state, even if he were to fast his whole life; if Allah wills He will forgive him, and if He wills He will punish him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9540