Abu Huraira reported God’s messenger as saying, “If anyone breaks his fast one day in Ramadan without a concession* or without being ill, a perpetual fast will not atone for it even if he observes it.”
*e.g. while travelling.
Ahmad, Tirmidhi, Abu Dawud, Ibn Majah, Darimi and Bukhari in a chapter heading transmitted it. Tirmidhi said that he heard Muhammad, i.e. Bukhari, say this was the only tradition he knew by Abul Mutawwis the transmitter.