Assalaamu alaykum. Is the following statement considered slander, bad thought, or accusing another in a scenario in which the reality is opposite to the statement: “I think he said something (and thereafter this issue was raised and became a problem, because it happened after we had somewhat of a confrontation)” - i.e. the reality is that the person did not say anything, so is the person who made this statement sinful, and if so, then what is the expiation? May Allah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

Attributing false statements to others deliberately falls into the category of the prohibited lying. If such false statements are libelous and include disliked information about the accused person, it is considered slander, which is the worst type of lying.

The author of Bareeqah Mahmoodiyyah said, "The gravest kind of lying is Buhtaan (slander), which means attributing to someone what he did not say or do and describing him with something disliked that is not actually in him." Committing Buhtaan against the believers involves having bad thoughts of them, which is prohibited as well.

It is incumbent on the person who has committed such a sin to repent to Allah of it and seek the pardon of the falsely accused person if there is no fear of Fitnah (any kind of harm) as a result; otherwise, he should supplicate Allah in favor of that person, seek forgiveness for him, and say that he was wrong about what he said among those who heard him say it.

Bareeqah Mahmoodiyyah reads, "Repentance from Buhtaan has three conditions: 1) Resolving not to commit this sin again. 2) Seeking the pardon of the falsely accused person if he is alive and reachable, if this would not incur Fitnah; otherwise, he should supplicate Allah in his favor, seeking forgiveness for him, and invoke Allah to pardon his sinful act. 3) Proclaiming the untruthfulness of such false accusations among those whom he informed (about the falsely accused person), because he committed Buhtaan."

Allah knows best.