Israaf in belief and actions

Until now we have discussed extravagance in monetary terms but since the dictionary meaning of Israaf is "exceeding limits" and "extremism" the same laws apply to beliefs and actions. Israaf in belief implies believing about oneself or others something that is untrue and inappropriate. For example the belief of Firon that he was God. As he told the people, 'I do not know any of the gods except myself.' The Almighty Allah has mentioned him as 'one who crossed the limits.'

"...surely Firon was lofty in the land; and most surely he was of the extravagant."
(Surah Yunus 10:83)

Regarding those who do not believe in Allah, Prophethood, Imams, Qiyamat etc.

The Almighty Allah says in the Holy Quran, 
"And thus do We recompense him who is extravagant and does not believe in the communications of his Lord; and certainly the chastisement of the Hereafter is severer and more lasting." 
(Surah Taha 20:127)

Performing detestable acts and avoiding advisable deeds is Israaf in action. For example the homosexual inclinations of the people of Prophet Lut (a.s.) have been termed as extravagance: 
"Most surely you come to males in lust besides females; nay, you are an extravagant people." 
(Surah Araaf 7:81)

In fact all the sins of actions and speech are a kind of extremism and every sinner is said to have crossed the limits. The Almighty says: 
"Say: O my servants! Who have acted extravagantly against their own souls, do not despair of the Mercy of Allah; surely Allah forgives the faults altogether; surely He is the Forgiving, the Merciful."
(Surah Zumar 39:53)

But we must not despair of our deficiencies. If we turn to Allah He shall certainly forgive. We on our part should make a sinceretoil not to be wasteful in our daily lives and not to exceed the limits in whatever we are engaged in. Moderation has to be practiced by us even in routine acts like eating, sleeping and talking. As the tradition says, 
"Verily Allah hates the one who eats excessively and the one who sleeps excessively."

For those who wish to study the subject in more detail we recommend the book Me'rajus Sa'adat. This book discusses the method of living in accordance with Islamic principles.