"'Adi bin Thabit and 'Ata bin As-Sa'ib informed me, from Sa'eed bin Jubair, from Ibn 'Abbas - and one of them mentioned that it was from the Prophet ﷺ - that he mentioned that Jibra'il began shoving clay in the mouth of Fir'awn out of fear that he would say La Ilaha Illallah and Allah would have mercy upon him - or fearing that Allah would have mercy upon him."  

عَنِ النَّبِيِّ ﷺ أَنَّهُ ذَكَرَ أَنَّ جِبْرِيلَ ﷺ جَعَلَ يَدُسُّ فِي فِي فِرْعَوْنَ الطِّينَ خَشْيَةَ أَنْ يَقُولَ لاَ إِلَهَ إِلاَّ اللَّهُ فَيَرْحَمَهُ اللَّهُ أَوْ خَشْيَةَ أَنْ يَرْحَمَهُ اللَّهُ  

[Machine] The Prophet Muhammad ﷺ said, "Indeed, the angel Gabriel ﷺ inserted his hand into Pharaoh's mouth out of fear that he might say, 'There is no god but Allah,' so that Allah, the Mighty and Majestic, may have mercy on him."  

عَنْ رَسُولِ اللَّهِ ﷺ قَالَ إِنَّ جِبْرِيلَ عَلَيْهِ السَّلَامُ جَعَلَ يَدُسُّ فِي فَمِ فِرْعَوْنَ الطِّينَ خَشْيَةَ أَنْ يَقُولَ لَا إِلَهَ إِلَّا اللَّهُ فَيَرْحَمَهُ اللَّهُ ﷻ  

"إِنَّ جبريلَ جعل يدُسُّ في فَم فرْعوْن الطِّينَ خَشْيةَ أَنْ يقولَ: لا إِلَه إِلا اللَّهُ فَيرْحمهُ اللَّهُ".