Plato, Letters 360e

μάνθανε παρʼ αὐτοῦ καὶ τἆλλα φιλοσόφει· εἰ δὲ μή, ἐκδίδαξαί τινα, ἵνα κατὰ σχολὴν μανθάνων βελτίων γίγνῃ καὶ εὐδοξῇς, ὅπως τὸ διʼ ἐμὲ ὠφελεῖσθαί σοι μὴ ἀνιῇ. καὶ ταῦτα μὲν δὴ ταύτῃ.

to take lessons from him in addition to your other studies in philosophy; but if not, get someone else thoroughly taught so that you may learn from him when you have leisure, and thereby make progress and gain glory,—that so the benefit you gain from me may still continue. So much, then, for this subject.