Ibn Abbas's View Regarding the Repentance of a Murderer
The brother is asking about the position of Ibn Abbas (may Allah be pleased with him) on the issue of the murderer and whether he has no repentance — and some groups have understood from this that Ibn Abbas considered the murderer to be a disbeliever (kafir). This is a mistake, and it is one of the scholarly errors that many scholars and jurists have repeated. Ibn Abbas (may Allah be pleased with him) did not say that, and not a single word has been authentically attributed to him to the effect that he declared the murderer a disbeliever.
What is authentically reported from Ibn Abbas is that he said: "He has no repentance." There is a difference between the two issues, and a difference between the two statements. Ibn Abbas is saying that the victim must receive his due right, and that if the murderer repents, the right of the victim's heir must still be fulfilled. That is the position (madhhab) of Ibn Abbas (may Allah be pleased with him). Even so, there is a second narration from him that aligns with the view of the majority.
In al-Bukhari's Al-Adab al-Mufrad with a sound chain, it is narrated that a man came to Ibn Abbas and said: "O Ibn Abbas, I have killed a soul — is there any repentance for me?" Ibn Abbas (may Allah be pleased with him) replied: "Do you have a mother?" The man said: "No." Ibn Abbas then instructed him to draw closer to Allah through whatever acts of goodness and worship he was capable of. When the man had left, one of Ibn Abbas's companions said: "O Ibn Abbas, why did you ask whether he had a mother?" He replied: "I know of no righteous deed that expiates this like devotion to her." — and this is explicit. Of course, this is a sound and explicit chain.
So Ibn Abbas did not hold that the murderer was a kafir. Secondly, he held that there was expiation for it — namely, righteous treatment of one's mother. The difference between Ibn Abbas and the majority is that the majority hold that the murderer has a valid repentance, while he held that he does not — but nothing is attributed to him declaring the murderer a disbeliever. There is a difference between the two statements. To say that Ibn Abbas declared the murderer a kafir is incorrect and inaccurate, and nothing of the sort has been attributed to him.