What is the difference between a sayyi'ah (evil deed) and a dhanb (sin), how does a person expiate for them, and do sins prevent the acceptance of good deeds?

The terms "Dhanb" (sin) and "Sayyi'ah" (evil deed) are used to describe the transgression of Allah's commands. Some scholars are of the view that "Dhanb" refers to major sins (Kaba'ir) and "Sayyi'ah" pertains to minor sins (Sagha'ir). Others believe that "Dhanub" are errors between a servant and his Lord, while "Sayyi'at" are errors related to the rights of people. Still, others hold that both terms carry the same meaning and their usage varies depending on the context.

Sins are expiated in this world through sincere repentance (Tawbah Nasuh) and seeking forgiveness (Istighfar), as well as by performing good deeds (Hasanat) that efface evil deeds. Among the righteous actions that expiate sins are performing Qiyam Ramadan (night prayers in Ramadan) and Qiyam Laylat al-Qadr (night prayers on the Night of Decree) out of faith and hope for reward. Prayers (Salat), Friday prayers (Jumu'ah), and Ramadan expiate what is between them, provided major sins are avoided. Furthermore, patience in the face of calamities and worries, and contentment with Allah's decree, expiate evil deeds.

According to the Ahl al-Sunnah wa al-Jama'ah (Sunni Muslims), it is not a condition for the acceptance of good deeds to avoid all transgressions. Rather, a deed is accepted from whoever fears Allah in it and performs it purely and in accordance with His command, even if they are disobedient in other matters. However, some deeds may require the abandonment of specific sins as a condition for their acceptance.