Passage 5.15.9
ἐν δὲ αὐτῷ τῷ πρυτανείῳ παριόντων ἐς τὸ οἴκημα, ἔνθα σφίσιν ἡ ἑστία, Πανός ἐστιν ἐν δεξιᾷ τῆς ἐσόδου βωμός. ἔστι δὲ ἡ ἑστία τέφρας καὶ αὕτη πεποιημένη, καὶ ἐπʼ αὐτῆς πῦρ ἀνὰ πᾶσάν τε ἡμέραν καὶ ἐν πάσῃ νυκτὶ ὡσαύτως καίεται· ἀπὸ ταύτης τῆς ἑστίας τὴν τέφραν κατὰ τὰ εἰρημένα ἤδη μοι κομίζουσιν ἐπὶ τὸν τοῦ Ὀλυμπίου βωμόν, καὶ οὐχ ἥκιστα ἐς μέγεθος συντελεῖ τῷ βωμῷ τὸ ἀπὸ τῆς ἑστίας ἐπιφορούμενον.
In the Prytaneion itself, as one enters the chamber in which their hearth is located, there is an altar of Pan on the right side of the entrance. This hearth also is made of ashes, and upon it a fire burns similarly throughout each day and every night. From this hearth they take ashes, according to the practice already described by me, and carry them to the altar of Olympian Zeus; indeed, the ashes brought from the hearth especially contribute to the size of the altar.