Muawiyah bin Qurrah narrated from his father (Sayyiduna Qurrah, may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: "Fasting on the white days is equal to fasting the whole year, even if you break your fast." («كما قال الشيخ أحمد الساعاتي فى الفتح الرباني 157/9»).
(Explanation of Ahadith 1782 to 1785) By «أيام البيض» is meant the 13th, 14th, and 15th dates of every month. In some narrations, it is also mentioned that the Messenger of Allah (sallallahu alayhi wa sallam) would fast on the first, second, and third dates of every month, but fasting in the middle of the month is more well-known. These are the fasts of three days, and under «﴿مَنْجَاءَبِالْحَسَنَةِفَلَهُعَشْرُأَمْثَالِهَا ...﴾ [الانعام : 160]» the reward is as if one has fasted for thirty days. Now, whoever fasts three days in every month, it is as if he has fasted the whole year, and he will receive the reward of fasting the entire year, even if he does not fast for the remaining twenty-seven days; the reward of fasting will continue to be given, except for the fasts of Ramadan, because fasting the entire month of Ramadan is obligatory. In Ramadan, fasting only three days would be contrary to the Shari‘ah.