An ascetic is steadfast in fulfilling his or her responsibilities, is not defeated by misfortune, and who avoids the traps of sin and evil encountered during the journey. With the exception of unbelief and misguidance, an ascetic is pleased with how the Creator decides to treat him or her, seeks to attain God's pleasure and the eternal abode through the blessings and bounties the He bestows, and directs others to the absolute Truth. In the ear of his or her heart, the Divine announcement is echoed: Say: The enjoyment of this world is short; and the Hereafter is better for him who obeys God's commandments in fear of Him (4:77). The command: Seek the abode of the Hereafter in that which God has given you, and forget not your portion of the world (28:77) radiates itself through all the cells of his or her brain. The Divine warning: This life of the world is but a pastime and a game, but the home of the Hereafter, that is Life if they but knew (29:64) penetrates his or her innermost senses.
Some have described asceticism as observing the rules of Shari'a even in moments of depression and especially during financial difficulties, and living for others or considering their well-being and happiness while enjoying well-being and comfort. Others have defined it as thankfulness for God's bounties and fulfilling the obligations that these bounties bring with them, and as refraining from hoarding money and goods (except for the intention to serve, exalt, and promote Islam).
Such renowned Sufi leaders as Sufyan al-Thawri regarded asceticism as the action of a heart set up according to God's approval and pleasure and closed to worldly ambitions, rather than as being content with simple food and clothes.  According to these Sufis, there are three signs of a true ascetic: feeling no joy at worldly things acquired or grief over worldly things missed, feeling no pleasure when praised or displeasure when criticized or blamed, and preferring to serve God over every other thing.
Like fear and hope, asceticism is an action of the heart; however, asceticism differs in that it affects one's acts and is displayed through them. Whether consciously or unconsciously, a true ascetic tries to follow the rules of asceticism in all acts, such as eating and drinking, going to bed and getting up, talking and keeping silent, and remaining in retreat or with people. An ascetic shows no inclination toward worldly attractions. Rumi expresses this in the following apt words:
What is the world? It is heedlessness of God;
Not clothes, nor silver coin, nor children, nor women.
If you have worldly possessions in the name of God,
Then the Messenger said: How fine is the property a righteous man has! 
The water in a ship causes it to sink,
While the water under it causes it to float.
Having worldly means or wealth are not contrary to asceticism if those who possess them can control them and are not overpowered by them. Nevertheless, the glory of humanity, upon him be peace and blessings, the truest ascetic in all respects, chose to live as the poorest of his people, for he had to set the most excellent example for his community especially for those charged with propagating and promoting the truth. Thus, he would not lead others to think that the sacred mission of Prophethood could be abused to earn worldly advantage.
He also had to follow his predecessors, who proclaimed: My reward is only due from God (10:72; 11:29), and to set an example for those future scholars who would convey his Message. For these and similar other reasons, he led an austere life. How beautiful are the following couplets by Busayri, which express how the Prophet preserved his innocence and indifference even at the time of absolute need and poverty:
Not to feel hunger, he wound a girdle around his belly
Over the stones pressing upon his blessed stomach.
Huge mountains wishing themselves gold offered themselves to him,
But he that noble man remained indifferent to them.
His urgent needs decisively showed his asceticism,
For those needs were not able to impair his innocence.
How could needs have been able to invite to the world the one
But for whom the world would not have come into being out of non-existence?
There are many beautiful sayings on asceticism. The following, with which we conclude this topic, belongs to 'Ali, the fourth Caliph and cousin of the Prophet, upon him be peace and blessings:
The soul weeps in desire of the world despite the fact that
It knows that salvation lies in renouncing it and what is in it.
A man will have no abode to dwell in after his death
Except that which he builds before he dies.
Our goods we hoard them to bequeath to heirs;
Our houses we build them to be ruined by time.
There are many towns built and then ruined;
Their builders death has come upon them.
Every soul even if it somehow fears death,
It cherishes ambitions to strengthen its desire to live.
Man exhibits his ambitions but time obliterates them;
Man's soul multiplies them but death puts an end to them.
O God! Show us truth as true and enable us to follow it. Show us falsehood as false, and provide us with the means to refrain from it. Amen, O Most Compassionate of the Compassionate.
 Ahmad ibn Hanbal, Musnad, 4.197.