"And the magicians fell down in prostration," meaning: they fell [to the ground]; so Pharaoh was confounded, and he let Musa go and did not interfere with him.
﴿فألقي السَّحَرَة ساجدين﴾ أَيْ: خَرُّوا؛ فَبُهِتَ فِرْعَوْنُ، وَخَلَّى سَبِيلَ مُوسَى وَلَمْ يَعْرِضْ لَهُ.