Seneca's Letters from a Stoic

Epistulae Morales ad Lucilium better known as Letters from a Stoic, is a collection of letters by Seneca the Younger. Seneca is one of the top Stoic writers, but this book contains ~30 quotations of Epicurus.

“I read today, in his works, the following sentence: “If you would enjoy real freedom, you must be the slave of Philosophy.” The man who submits and surrenders himself to her is not kept waiting; he is emancipated on the spot. For the very service of Philosophy is freedom.” – Seneca Letters – Book I https://en.wikipedia.org/wiki/Epistulae_Morales_ad_Lucilium