Question 16: I started fasting the six days of Shawwaal when some circumstances and business interrupted me. I could not fast the remaining two days. What can I do? Should I make up for missing these two days? Will I incur a sin for not completing the six days?
Answer: Fasting the six days of Shawwaal is a Mustahab (desirable) act of worship but is not Waajib (obligatory). You will receive the reward of the days on which you fasted and hopefully you will receive the full reward of fasting the six days, if you had a Shar‘ee (Islaamic legal) excuse for not completing them. The Prophet (peace be upon him) said: When a servant (of Allaah) falls ill or travels, the same reward of the good deeds they used to do when at home in good health is recorded for them. (Related by Al-Bukhaaree in his Saheeh [Authentic Hadeeth Book]) You do not have to make up for those two missed days... read more here.