Assalamy alaykum warahmatullahi wabarakatuhu. What is excesiveness in Islam? How to know how much activity (be it religious or wordly) is too much? Is it a sin to do certain activities till your exhaustion?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Excessiveness is a propensity to exaggerate, which is exceeding the limits set by Sharee'ah in praising or condemning something over what it deserves or adding in worship, for example, over what the Sharee'ah demands. The Messenger has forbidden it. It is reported in the Sunan of Ibn Maajah and others that the Prophet said: “O people, beware of exaggeration in religious matters, for those who came before you were doomed because of exaggeration in religious matters.” Al-Albani graded it Sahih (authentic). Therefore, exaggeration is forbidden in belief and in actions.

One of its forms is the exaggeration about the prophets and the righteous people by considering them in the position of the Lord, such as seeking help from them and asking them for what only Allah is capable of.

The discussion of extremism in religion, its criteria, and its forms takes time, and a Fatwa is not enough for it. A Fatwa can only cover some individual aspects that might be confusing to the questioner, whether it is a form of extremism or not. If you want to expand on the topic of extremism, you can read some of the books in this field.

As for whether a person bears a sin if he performs an activity until exhaustion or not; if by the activity you mean worship, then it is disliked that a person burdens himself with more than what he can bear of worship. Al-Bukhari titled a chapter in his Sahih: The chapter on what is disliked about strictness in worship. In this chapter, he mentions the Hadith of Anas ibn Malik . He said: “Once, the Prophet entered the Mosque and saw a rope hanging in between its two pillars. He said, “What is this rope?” The people said, “This rope is for Zainab who, when she feels tired, holds it (to keep standing for the prayer.)” The Prophet said, “Don't use it. Remove the rope. You should pray as long as you feel active, and when you get tired, sit down.” He also mentions the Hadith of 'Aaishah . She said: “A woman from the tribe of Bani Asad was sitting with me and Allah's Messenger came to my house and said, “Who is this?” I said, “(She is) So-and-so. She does not sleep at night because she is engaged in prayer.” The Prophet said disapprovingly: Do (good) deeds which are within your capacity as Allah never gets tired of giving rewards till you get tired of doing good deeds.”

The interpreters of Hadith said: “Being too strict in matters of worship is disliked for fear of apathy and boredom.” [End of quote].

Allah knows best.