Enneads I.9: Of Suicide
Voluntary Soul-detachment Is Forbidden
One may not voluntarily disengage oneself from the fetters of the body. When violence is employed, it is not the body which disengages itself from the soul, it is the soul which makes an effort to snatch herself from the body, and that by an action which accomplishes itself not in the state of impassibility (which suits a sage), but as the result of grief, or suffering, or of anger. Now such an action is forbidden, or unworthy.
May one not forestall delirium or insanity, if one become aware of their approach? To begin with, insanity does not happen to a sage, and if it does, this accident should be considered one of those inevitable things which depend from fatality, and in which case one should direct one's path less according to his intrinsic quality than according to circumstances; for perhaps the poison one might select to eject the soul from the body might do nothing but injure the soul.
If there be an appointed time for the life of each of us, it is not well to forestall the decree of Providence, unless, as we have said,[328] under absolute compulsion.
Last, if rank obtained above depend on the state obtaining at the time of exit from the body, no man should separate himself from it so long as he might still achieve progress.[329]