Source for (Stoic?) quote on death/(im)mortality

Question

In Eckhart Tolle's book The Power of Now, there is the following fragment of a question that the author was asked:

I read about a stoic philosopher in ancient Greece who, when he was told that his son had died in an accident, replied, "I knew he was not immortal."

The quote that is mentioned sounds very much like something a Stoic would say and it resonates with me and helps me to remember the mortality of myself and those around me. But I cannot find a source for this quote. Can someone help me? Maybe it was something Epictetus said, hidden somewhere in his Discourses, or perhaps Seneca uses it as an anecdote somewhere? Or perhaps it was someone else entirely, perhaps not even a Stoic... If anyone has a clue, I would very much appreciate it :)

Answer 1

Your quote is attributed to the Greek general Xenophon. It's written in "Lives of Eminent Philosophers" by Diogenes Laërtius:

In this battle Epaminondas also fell. On this occasion Xenophon is said to have been sacrificing, with a chaplet on his head, which he removed when his son's death was announced. But afterwards, upon learning that he had fallen gloriously, he replaced the chaplet on his head. Some say that he did not even shed tears, but exclaimed, "I knew my son was mortal." Source

Answer 2

The Enchiridion of Epictetus contains a number of comments very close to this. It is possible that there is another source that gets even closer to your quotation, but I wonder if Tolle is thinking of these comments of Epictetus and paraphrasing them, or not remembering them precisely. (And of course, I am relying on a translation, too!) Here are some of the claims from the version of the text at the Internet Classics Archive:

Epictetus instructs us that we remember that our children are merely human, and that while we appreciate them as examples of humanity, we should accept that it is unreasonable to be overly attached to them in particular:

3. With regard to whatever objects give you delight, are useful, or are deeply loved, remember to tell yourself of what general nature they are, beginning from the most insignificant things. If, for example, you are fond of a specific ceramic cup, remind yourself that it is only ceramic cups in general of which you are fond. Then, if it breaks, you will not be disturbed. If you kiss your child, or your wife, say that you only kiss things which are human, and thus you will not be disturbed if either of them dies.

He recommends avoiding the attitude of attachment or ownership toward our family members:

11. Never say of anything, "I have lost it"; but, "I have returned it." Is your child dead? It is returned. Is your wife dead? She is returned.

Elaborating on the theme of not imagining that we own our children or deserve to have them but here connecting it with immortality, this line is perhaps closest to the one you ask about:

14. If you wish your children, and your wife, and your friends to live for ever, you are stupid; for you wish to be in control of things which you cannot, you wish for things that belong to others to be your own.