مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2140
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas - he said: One of them attributed it to the Prophet (ﷺ) - said: "Jibreel was shoving mud intro Pharaoh's mouth, lest he say La ilaha illallaah."
Musnad Ahmad 2144Saheeh mawqoof]