Allah says:

فَأُلْقِيَ السَّحَرَةُ سَاجِدِينَ ﴿٤٦﴾

قَالُوا آمَنَّا بِرَبِّ الْعَالَمِينَ ﴿٤٧﴾

رَبِّ مُوسَى وَهَارُونَ ﴿٤٨﴾

And the sorcerers fell down prostrate. Saying: "We believe in the Lord of Al-`Alamin, the Lord of Musa and Harun.''

This is as Allah mentions elsewhere:

فَوَقَعَ الْحَقُّ وَبَطَلَ مَا كَانُواْ يَعْمَلُونَ

فَغُلِبُواْ هُنَالِكَ وَانقَلَبُواْ صَاغِرِينَ

وَأُلْقِيَ السَّحَرَةُ سَاجِدِينَ

قَالُواْ آمَنَّا بِرِبِّ الْعَالَمِينَ

رَبِّ مُوسَى وَهَارُونَ

Thus truth was confirmed, and all that they did was made of no effect. So they were defeated there and returned disgraced. And the sorcerers fell down prostrate. They said: "We believe in the Lord of all that exists, the Lord of Musa and Harun.'' (7:118-122)

This was a very serious matter, furnishing decisive proof leaving no room for any excuse. Fir`awn's supporters, who sought and hoped that they would prevail over Musa, were themselves defeated. At that moment they believed in Musa and prostrated to Allah, the Lord of Al-`Alamin Who sent Musa and Harun with the truth and an obvious miracle. Fir`awn was defeated in a manner the likes of which the world had never seen, but he remained arrogant and stubborn despite the clear evidence, may the curse of Allah and the angels and all of mankind be upon him. He resorted to arrogance and stubbornness and propagating falsehood. He began to issue threats against them, saying:

إِنَّهُ لَكَبِيرُكُمُ الَّذِى عَلَّمَكُمُ السِّحْرَ

Verily, he is your chief who has taught you magic. (20:71)

إِنَّ هَـذَا لَمَكْرٌ مَّكَرْتُمُوهُ فِى الْمَدِينَةِ

Surely, this is a plot which you have plotted in the city. (7:123)