Parikuppa Sutta (AN 5:129)
This discourse lists the five grave deeds that are said to prevent one’s chances of attaining any of the noble attainments in this lifetime. People who commit them fall—immediately at the moment of death—into hell. No help from outside is able to mitigate the sufferings they will endure in hell, and thus they are said to be incurable. Only when the results of these deeds have worked themselves out will they be released from hell. Even if they return to the human plane, they will continue to suffer the consequences of their deeds. For example, Ven. Moggallāna, one of the Buddha’s foremost disciples, killed his parents many eons ago, and the results of that deed pursued him even through his final lifetime, when he was beaten to death.
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“There are these five inhabitants of the states of deprivation, inhabitants of hell, who are in agony & incurable. Which five? One who has killed his/her mother, one who has killed his/her father, one who has killed an arahant, one who—with a corrupted mind—has caused the blood of a Tathāgata to flow, and one who has caused a split in the Saṅgha. These are the five inhabitants of the states of deprivation, inhabitants of hell, who are in agony & incurable.”
See also: MN 130