An-Nawwas ibn Sam’aan reported that Prophet Muhammad said:

"Righteousness is good character, and sin is whatever bothers you and you do not want people to know." (Saheeh Muslim)

An-Nawwas ibn Sam’aan is a famous companion of Prophet Muhammad.  He belonged to the Arab tribe of Kelaab and settled in Syria after the death of the Prophet.

His report is collected by a scholar of hadeeth named Muslim ibn Al-Hajjaj, who was born in 817 CE in the city of Naishapur, in north-eastern Iran, and died there at the age of 58, in 875 CE.  Muslim began studying the science of Prophetic hadeeth at the age of 15 and traveled to Iraq, Hijaz (Western Saudi Arabia), Syria, and Egypt to study under great hadeeth masters like al-Bukhari, Ahmad ibn Hanbal, and others.  He compiled a book containing some 9,200 hadeeths which is known as Saheeh Muslim.  Muslim scholars consider it to be the most authentic compilation of Prophetic hadeeths after Saheeh al-Bukhari.

This narration is important in that it sheds light on some of the more subtle aspects of righteousness and sin, helping to define them both.  Since Islam gives so much importance to the belief in and worship of One God, one may incorrectly think that this alone is enough to be righteous.  This hadeeth, however, shows that one of the main consequences of correct and true belief is good character, and that it is an intrinsic aspect of the meaning of righteousness.  It emphasizes some of the meanings found in the saying of God which mentions that righteousness, as well as a being a combination of correct belief and prescribed worship, is also proper conduct in human relations:

"Righteousness is not that you turn your faces to the east and the west [in prayer].  But righteous is the one who believes in God, the Last Day, the Angels, the Scripture and the Prophets; who gives his wealth in spite of love for it to kinsfolk, orphans, the poor, the wayfarer, to those who ask and to set slaves free.  And (righteous are) those who pray, pay alms, honor their agreements, and are patient in (times of) poverty, ailment and during conflict.  Such are the people of truth.  And they are the God-Fearing." (Quran 2:177)

Rather than being an end in itself, one of the main purposes of worship is to bring about traits beneficial to the self and society.  God says about the salah (prayer):

"Surely, the salah prevents lewd acts and bad deeds…" (Quran 29:45)

Hence one can say without any qualms that Islam as a whole came to perfect good manners, as did the Prophet himself:

"Indeed I was only sent to complete the most noble character traits." (Saheeh Muslim)

As Islam is not a mere religion but a complete way of life, incorporating all of its various facets and aspects, good manners is actually regarded as a means of worship by which one may achieve the same reward of doing other more obvious voluntary acts of worship.  The Prophet, may the mercy and blessings of God be upon him, stated:

"Through his manners and good conduct, the believer can attain the status of a person who frequently fasts and prays at night." (Abu Dawud)

Rather, the Prophet even stated it to be one of the best forms of worship, second to none but the obligatory mandates of Islam:

"On the Day of Resurrection, nothing will be heavier in the scale (of good deeds) of the believer than good conduct.  God hates the one who swears and hurls obscenities." (Abu Dawud, Al-Tirmidhi)

Through maintaining good conduct, one becomes one of the beloved servants of God.  The Prophet said:

"The most beloved slaves of God to God are those who have the best manners." (Al-Hakim)

When one realizes the importance of good character and its essentiality in defining righteousness, an aspect which is the goal of Islam, this exhorts Muslims to fulfill this aspect of faith as well, since one can not become "righteous" through mere belief and devotion to God in themselves without good character.

But what is regarded as good character?  We find that the Quran and Sunnah in various texts define it to be any trait that is beneficial to humans, both to oneself as well as to others, at the same time not being generally or specifically prohibited by Islam.  For example, God says:

"Those who suppress their anger, and forgive other people – assuredly, God loves those who do good." (Quran 3:134)

Righteousness is dealing fairly, justly and politely with one’s family.  The Prophet said:

"The believers with the most perfect faith are those with the most perfect conduct and manners.  And the best ones amongst you are those who are best to their families." (Al-Tirmidhi)

Truthfulness is an essential aspect of good character which leads to Paradise.  The Prophet said:

"Indeed truthfulness is righteousness, and indeed righteousness leads to Paradise." (Saheeh Muslim)

These are but a few examples of the numerous texts which define and exhort Muslims to excel in their character and manner.  Although righteousness is those deeds which are naturally pleasing to the conscience of humans, religion plays a vital role in defining what it is.  For example, anything of which its harm is greater than its good cannot be defined as righteousness, even if it may be otherwise regarded as goodness and righteousness.  The Prophet said:

"It is not righteousness that you fast during travel." (Saheeh Al-Bukhari)

Although fasting is one of the most meritorious of deeds, here it is not considered righteousness due to the harm it may incur to the individual and his comrades during a journey.  Also, to steal from the rich in order to give to the poor may not be regarded as righteousness, as stealing has been specifically prohibited in the religion.

At the same time, a deed which may sometimes be seen as harsh may also be considered good character at times, such as striking a child at a certain age as a means of education.  The Prophet said:

"Command your children to pray when they are seven, and strike them [if they do not] when they are ten…" (Abu Dawud)

For this reason, we look to divine guidance in order to define for us good manners and character, exemplified by the Prophet, as God said:

"Surely, you (O Muhammad) are upon a high standard of moral character." (Quran 68:4)

God also said:

"Indeed in the Messenger of God you have a beautiful example of conduct to follow…" (Quran 33:21)

Aisha, the wife of the noble Prophet, was asked about his character.  She replied:

"His character was that of the Quran." (Saheeh Muslim, Abu Dawud)