If someone misses ten days of fasting in Ramadan due to a Shar‘y (Islamic legal) excuse, and then fasts the six days of Shawwal after Ramadan without making up for the missed days of Ramadan,
will they attain the Thawab (reward from Allah) promised for fasting the whole month of Ramadan then following it with fasting the six days of Shawwal? Will it be as if they have fasted for the whole year? Guide us, and may Allah reward you with the best.
Determining the rewards of the deeds performed by a servant of Allah is the special domain of Allah (Glorified and Exalted be He). If a servant seeks the reward of Allah (Glorified and Exalted be He), and exerts themselves in their obedience to Allah, their reward will not be lost. Allah (Exalted be He) says:
...certainly We shall not make the reward of anyone who does his (righteous) deeds in the most perfect manner to be lost.
Anyone who still has missed days of Ramadan which they need to make up for should first (Part No. 10; Page No. 393) fast them, and then fast the six days of Shawwal. Following the Sawm (Fast) of Ramadan with six days of Shawwal will not be fulfilled unless one has first completed the Sawm of Ramadan.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.