Reference for Makkot 27:1

כדאמרינן מעיקרא שאם עשו תשובה ב"ד של מעלה מוחלין להן מאי אמרת הא לא עבוד תשובה לא פסיקא מילתא לכרת

[the dispute] is as we said previously, that [Rebbi Akiva's reason for giving malkus by liabilities of kares is that] if he repents the heavenly court will forgive him. What did you ask? That he hasn't yet repented? Kares is not definite. [He can still repent.]

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