فَتَنَازَعَا سَبْطًا يَطِيرُ ظِلَالُهُ ۞ كَدُخَانِ مُشْعَلَةٍ يَشُبُّ ضِرَامُهَا
The two rushed forward, raising a long trail of dust whose dark spread rose like smoke from a fiercely burning fire.
Fa-tanāzaʿā depicts the pair striving or racing together. Sabṭan is explained as a long, extended plume of dust. Ka-dukhāni mushʿalah supplies the simile: earthbound dust is pictured as smoke rising above a vigorous fire.