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Major sins includes (but is not limited to) the following acts:
Worshiping others, or associating partners with Allah (shirk)
Believing in superstition, fortune telling and astrology
Using magic or sorcery
Committing murder
Committing suicide
Bearing false witness
Committing adultery or fornication
Cheating, stealing, and lying
Charging or paying interest or usury (riba)
Consuming pork or alcohol
Consuming the wealth of an orphan
Not fasting for Ramadan
Not observing daily prayers
Not paying zakat (annual charity)
Gambling
Oppression and unjust leadership
Bribery, betraying trusts and breaking contracts
Backbiting and slandering
Breaking the ties of kinship
Disobeying or not honoring one’s parents
Minor Sins in Islam
Minor sins are acts which are displeasing to Allah but for which no specific punishment or severe warning has been issued. In this case, a Muslim’s conscience and heart help him to know that an act is sinful.
The Prophet Muhammad (peace be upon him) said, “Righteousness is good character, and sin is that which wavers in your heart and which you do not want people to know about.” (Muslim)
Minor sins are not, however, to be taken lightly, as disobeying Allah is always a serious matter. Allah says: “You counted it a little thing, while with Allah it was very great.” (Qur’an 24:15)
Minor sins can easily lead someone to commit a major sin, and repeatedly committing a minor sin will change its status to that of a major sin.
Furthermore, habitual sinning causes a Muslim to lose faith and disregard the commandments of Allah. In the Qur’an, Allah says: “Nay, their hearts have been sealed by the sins they have accumulated.” (Qur’an 83:14).
Forgiveness and Expiation in Islam
Scholars agree that while good deeds and extra acts of worship help expiate minor sins, they won’t compensate for major sins. Instead, a Muslim must make sincere repentance for major sins by showing genuine remorse, praying for Allah’s Mercy and Forgiveness, and avoiding that sin in the future.
Only a person who avoids major sins will have good deeds such as charity, praying, or fasting accepted as expiation for minor sins. Allah says: “If you shun the great sins which you are forbidden, We will do away with your small sins and cause you to enter an honorable place of entering.” (Qur’an 4: 31)
Shirk, however, is the one sin which Allah will not forgive. “Verily, Allah forgives not that partners be set up with Him (in worship) but He forgives other than that to whom He pleases; and whoever sets up partners with Allah (in worship), he has indeed invented an enormous wrong.” (Qur’an 4:48)
Sources:
موقع دعوي، علمي تربوي يهدف إلى تقديم الفتاوى والإجابات العلمية المؤصلة عن الأسئلة المتعلقة بالإسلام بشكل واف وميسر قدر الاستطاعة
islamqa.info
أول موقع عربي على الإنترنت يهتم بنشر الثقافة الإسلامية والتعريف بمبادىء الدين الحنيف عبر معالجة عالم الأفكار والاهتمام بالعلوم وإصدارات الكتب.
islamonline.net
Major Sins in Islam, Compiled and Translated into English by Muhammad Iqbal Siddiqi, International Islamic Publishers, New Delhi (1988).