Does one sin by leaving some of the voluntary acts that he used to perform regularly?

Q: The sister who used the code name Umm Yusuf from Makkah al-Mukarramah says in her question: Does a person sin by leaving some of the voluntary acts that he used to perform regularly? For example, during my pregnancy, I left fasting on Mondays and Thursdays. Please give us a ruling, may Allah reward you with good.

A: All voluntary acts are rewarded for the one who performs them, and the one who leaves them does not sin, such as fasting on Mondays and Thursdays, three days of every month, the sunnah of Dhuha, and the witr prayer. However, it is prescribed for the believer to be consistent and maintain the confirmed sunnahs, because of the great reward and abundant recompense therein, and because the voluntary acts complete the deficiency in the obligatory acts. And Allah is the One who grants success.