Tafsir: Al-A'raf 7:122

Next, the verse said:

فَوَقَعَ الْحَقُّ وَبَطَلَ مَا كَانُوا يَعْمَلُونَ ﴿118﴾ فَغُلِبُوا هُنَالِكَ وَانقَلَبُوا صَاغِرِ‌ينَ ﴿119﴾ وَأُلْقِيَ السَّحَرَ‌ةُ سَاجِدِينَ ﴿120﴾قَالُوا آمَنَّا بِرَ‌بِّ الْعَالَمِينَ ﴿121﴾ رَ‌بِّ مُوسَىٰ وَهَارُ‌ونَ ﴿122﴾

"So, the truth prevailed and what they were doing became a nullity. So there they were overcome and turned humiliated. And the sorcerers were constrained to fall in prostration. They said, "We believe in the Lord of the worlds, the Lord of Musa and Harun."

The sorcerers were so overawed by the miracle of the prophet Musa (علیہ السلام) that they fell in prostration. This may also imply that Allah blessed them with favour and put them in prostration. They added the phrase, the Lord of Musa and Harun (علیہما السلام) after saying, the Lord of the worlds, to make it clear that the Lord worshipped by Musa (علیہ السلام) and Harun (علیہ السلام) is, in fact, the Lord of the Universe, and not the Pharaoh as he pretended to be.