Molon labe significant event Battle of Thermopylae
Origin
Plutarch cites the phrase in his Apophthegmata Laconica ("Sayings of Spartans"). The exchange between Leonidas and Xerxes occurs in writing, on the eve of the Battle of Thermopylae (480 BC):πάλιν δὲ τοῦ Ξέρξου γράψαντος 'πέμψον τὰ ὅπλα,' ἀντέγραψε 'μολὼν λαβέ.' 
When Xerxes wrote again, 'Hand over your arms,' he wrote in reply, 'Come and take them.' (trans. Frank Cole Babbitt, 1931)
The exchange is cited in a collection of sayings by Leonidas before the Battle of Thermopylae (51.2–15).
The main source for the events of the battle is Herodotus. According to his account, the Spartans held Thermopylae for three days, and although ultimately defeated, they inflicted serious damage on the Persian army. Most importantly, this delayed the Persians' progress to Athens, providing sufficient time for the city's evacuation to the island of Salamis. Though a tactical defeat, Thermopylae served as a strategic and moral victory, inspiring the Greek forces to defeat the Persians at the Battle of Salamis later the same year and the Battle of Plataea one year later.