وَقَالَ فِرْعَوْنُ ذَرُونِىٓ أَقْتُلْ مُوسَىٰ وَلْيَدْعُ رَبَّهُۥٓ ۖ إِنِّىٓ أَخَافُ أَن يُبَدِّلَ دِينَكُمْ أَوْ أَن يُظْهِرَ فِى ٱلْأَرْضِ ٱلْفَسَادَ Qur’an Ghafir (40:26)Waqala firAAawnu tharoonee aqtul moosa walyadAAu rabbahu innee akhafu an yubaddila deenakum aw an yuthhira fee alardi alfasada
My interpolation of the word "alleged", is necessitated by the obvious sarcasm of Pharaoh's remark.
This is an episode that occurs when Moses, invested with his mission, confronts Pharaoh in his Court and preaches to him: see xx. 49 and following verses; also xx. 57, 63.
Some of Pharaoh's people did afterwards give up the worship of Pharaoh and of the Egyptian gods and believed "in the Lord of Aaron and Moses" and in fact suffered martyrdom for the Faith of Unity: xx. 70-73.