Is dereliction in the rights of Muslims, such as failing to say "yarhamukallah" to one who sneezes, to follow a funeral procession, or to return a greeting of peace, considered among the rights of people for which one will be held accountable on the Day of Resurrection and which will not be forgiven except by the forgiveness of the one whose right was violated?

The rights for which a person will be held accountable on the Day of Judgment, and which will not be forgiven except by the permission of the right-holder, are those whose violation results in injustice or harm to others. As for the rights of a Muslim mentioned in the Hadith (definition), they are not of this kind; rather, they are based on mutual forgiveness among people. According to the majority of scholars, these are not individual obligations, but rather pertain to manners and recommended acts, or communal obligations (fard kifaya).