Greek proverb: Μουσῶν θύραι

Here's a saying from Apostolius, C4.54, with a Latin version from Clavis Homerica. The image is by Raphael. Here are some more Apostolius proverbs.

Ἄφθονοι Μουσῶν θύραι.
Invidiae expertes Musarum fores.
The doors of the Muses are free of envy.