Phaedo - P:91

We must proceed, he said, and first remind me of what you said if I do not appear to remember it. Simmias, as I believe, is in doubt and fear that the soul, though it is more divine and beautiful than the body, yet predeceases it, being a kind of harmony. Cebes, I thought, agrees with me that the soul lasts much longer than the body, but that no one knows whether the soul often wears out many bodies and then, on leaving its last body, is now itself destroyed. This then is death, the destruction of the soul, since the body is always being destroyed.