Via the Laudator:
Epictetus, Discourses 3.5.5-6 (tr. W.A. Oldfather):
Do you not know that disease and death needs must overtake us, no matter what we are doing? They overtake the farmer at his work in the fields, the sailor on the sea. What do you wish to be doing when it overtakes you? For no matter what you do you will have to be overtaken by death. If you have anything better to be doing when you are so overtaken, get to work on that.
οὐκ οἶδας, ὅτι καὶ νόσος καὶ θάνατος καταλαβεῖν ἡμᾶς ὀφείλουσίν τί ποτε ποιοῦντας; τὸν γεωργὸν γεωργοῦντα καταλαμβάνουσι, τὸν ναυτικὸν πλέοντα. σὺ τί θέλεις ποιῶν καταληφθῆναι; τί ποτε μὲν γὰρ ποιοῦντά σε δεῖ καταληφθῆναι. εἴ τι ἔχεις τούτου κρεῖσσον ποιῶν καταληφθῆναι, ποίει ἐκεῖνο.