I say, and with God's success: The fasting of the six days of the month of Shawwal has great merit. Abu Ayyub Al-Ansari, may God be pleased with him, reported that the Prophet, peace be upon him, said: "Whoever fasts Ramadan and then follows it with six days of Shawwal, it is as if he has fasted for a lifetime." (Sahih Muslim 2: 822). Fasting in Shawwal is recommended; those who fast it will receive a reward, and those who do not fast it will not be punished. It is not necessary to fast all six days; one can fast some of them, as fasting some does not require fasting the rest. The last time to do so is the end of Shawwal, and God knows best.