The First Extra-Biblical Reference to the Sabbath, c. 630 BCE

The Mezad Hashavyahu Ostracon contains the first extra-biblical reference to the Sabbath-

Let my Lord Commander hear the case of his servant! As for thy servant, thy servant was harvesting at Hazar-Susim (?). And thy servant was (still) harvesting as they finished the storage of grain as usual before the Sabbath…