Letters 108.19

Pythagoras, on the other hand, held that all beings were inter-related, and that there was a system of exchange between souls which transmigrated from one bodily shape into another. If one may believe him, no soul perishes or ceases from its functions at all, except for a tiny interval—when it is being poured from one body into another. We may question at what time and after what seasons of change the soul returns to man, when it has wandered through many a dwelling-place; but meantime, he made men fearful of guilt and parricide, since they might be, without knowing it, attacking the soul of a parent and injuring it with knife or with teeth—if, as is possible, the related spirit be dwelling temporarily in this bit of flesh!

Seneca, Letters to Lucilius 108.19, translated by Richard Mott Gummere