﴿ وَإِذْ قُلْنَا لِلْمَلَٰٓئِكَةِ ٱسْجُدُوا۟ لِءَادَمَ فَسَجَدُوٓا۟ إِلَّآ إِبْلِيسَ أَبَىٰ وَٱسْتَكْبَرَ وَكَانَ مِنَ ٱلْكَٰفِرِينَ ﴾

“And when We told the angels, "Prostrate yourselves before Adam!" -they all prostrated themselves, save Iblis, who refused and gloried in his arrogance: and thus he became one of those who deny the truth.”

(And when We said unto the angels: Prostrate yourselves before Adam), a prostration of salutation, (they fell prostrate, all save Iblis. He demurred through pride) to follow his Lord's command. (And so became a disbeliever) after this because he refused to comply with Allah's command. It is also said that it was in Allah's foreknowledge that Satan was to become a disbeliever; as it is said that he was the first unbeliever ever.