Short answer
Minor sins (sagha'ir) are wrong acts below the level of a major sin, such as a lingering look at what is not allowed, harsh words or small habits of disobedience. Allah promises to wipe them away for those who avoid the major sins, and wudu, the five prayers, Jumu'ah and Ramadan erase them. But persisting in them, or taking them lightly, makes them grave.
Hanafi scholars divide sins into major and minor, following 4:31. Minor sins are expiated by good deeds and by avoiding the major sins, while repentance is still recommended from every sin. Persistence (israr) on a minor sin turns it into a major one.
The four schools agree on this.
Explanation
The Quran draws the line: "If you avoid the major sins which you are forbidden, We will remove from you your lesser sins" (4:31). It praises "those who avoid the major sins and immoralities, only [committing] slight ones" (53:32), and says "good deeds do away with misdeeds" (11:114).
The Prophet ﷺ said the five prayers, Jumu'ah to Jumu'ah and Ramadan to Ramadan wipe out what is between them, as long as the major sins are avoided. Sahih hadith also say that sins leave with the water of wudu, and that walking to the mosque raises rank and removes sins. That is how a Muslim's daily routine keeps cleaning the record.
What counts as minor? Scholars usually define it as a sin with no specific threat of Hell, curse or fixed punishment attached to it. Examples include a glance at something forbidden, speaking harshly, small acts of impatience, or a makruh tahrimi act done once. The Companion Anas told the next generation, in a report in al-Bukhari, that deeds they thought finer than a hair were counted in the Prophet's time among the destroyers. A sin looks small or big depending on how you see the One you disobey.
Scholars also said: there is no minor sin with persistence, and no major sin with sincere repentance. So do not stack up small sins. Read what are the major sins?, what deeds wipe away sins? and how to repent.
The evidence
Quran, Surah An-Nisaa 4:31
إِن تَجْتَنِبُوا۟ كَبَآئِرَ مَا تُنْهَوْنَ عَنْهُ نُكَفِّرْ عَنكُمْ سَيِّـَٔاتِكُمْ وَنُدْخِلْكُم مُّدْخَلًۭا كَرِيمًۭا ﴿٣١﴾
If you avoid the major sins which you are forbidden, We will remove from you your lesser sins and admit you to a noble entrance [into Paradise].
Promises forgiveness of minor sins to those who avoid the major ones.
Quran, Surah Hud 11:114
وَأَقِمِ ٱلصَّلَوٰةَ طَرَفَىِ ٱلنَّهَارِ وَزُلَفًۭا مِّنَ ٱلَّيْلِ ۚ إِنَّ ٱلْحَسَنَٰتِ يُذْهِبْنَ ٱلسَّيِّـَٔاتِ ۚ ذَٰلِكَ ذِكْرَىٰ لِلذَّٰكِرِينَ ﴿١١٤﴾
And establish prayer at the two ends of the day and at the approach of the night. Indeed, good deeds do away with misdeeds. That is a reminder for those who remember.
Shows good deeds erase minor sins.
Sahih Muslim 233
Sahih... مُكَفِّرَاتٌ مَا بَيْنَهُنَّ إِذَا اجْتَنَبَ الْكَبَائِرَ ...
"The five prayers, Jumu'ah to Jumu'ah and Ramadan to Ramadan wipe out what is between them, as long as the major sins are avoided."
Shows regular worship expiates minor sins.
Where the ruling is recorded
- Ihya Ulum al-Din (al-Ghazali), Book of repentance, on what makes minor sins grave. Explains how persistence and taking sins lightly make them major.
- al-Kaba'ir (al-Dhahabi), Introduction. Explains the difference between major and minor sins.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.