It is narrated from Hazrat Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: Whoever reaches the month of Ramadan and has some obligatory fasts from the previous Ramadan upon him which he has not made up, then his current fast will not be accepted. And whoever starts keeping voluntary fasts while he has some obligatory fasts of Ramadan upon him which he has not made up, then his voluntary fast will not be accepted until he completes the obligatory fasts.