Tafsir of Yunus 10:80

This is a conjunction connected to an implied element necessitated by the context, which has been omitted to signal the speed of their compliance with the command, as is the function of the fa of eloquence (al-fa' al-fasihah). An analogous example has been stipulated in His—the Exalted’s—saying: {فَقُلْنَا اضْرِب بِّعَصَاكَ الْحَجَرَ فَانفَجَرَتْ}, meaning: "So they brought them, and when they came..."

{قَالَ لَهُم مُّوسَىٰ أَلْقُوا مَا أَنتُم مُّلْقُونَ}

Meaning: What you have firmly resolved and decided to cast, whatever it may be among the varieties of sorcery. The root of al-ilqa' (casting) is to throw a thing where it is tulaqqahu—that is, where you see it—then it became, by convention, a name for any throwing. This statement from him (peace be upon him) came after they said to him what was narrated about them in other surahs, such as their saying: {إِمَّا أَن تُلْقِيَ وَإِمَّا أَن نَّكُونَ نَحْنُ الْمُلْقِينَ} and the like; it was not at the beginning of their arrival.

{مَا} is a relative pronoun, the sentence following it is the conjunctive clause, and the pronominal referent is omitted, meaning: mulqunahu (casting it). The vagueness here clearly serves to belittle and indicate a lack of concern. The intent is to command them to present what they had resolved to perform so that its falsehood might be exposed; it is not a command to perform sorcery or an endorsement of it.