It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him), attributing it to the Prophet (marfu'), that the Prophet (peace and blessings be upon him) was asked: Which prayer is most virtuous after the obligatory ones? And which fasting is most virtuous after Ramadan? He (peace and blessings be upon him) said: "The most virtuous prayer after the obligatory prayer is the prayer in the middle of the night, and the most virtuous fasting after Ramadan is the fasting of Allah's month, Muharram." This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.