رَبِّ اشْرَحْ لِي صَدْرِي، وَيَسِّرْ لِي أَمْرِي، وَاحْلُلْ عُقْدَةً مِنْ لِسَانِي، يَفْقَهُوا قَوْلِي
This is a Quranic supplication from Surah Ta-Ha (20:25-28), made by Prophet Musa (peace be upon him) when Allah commanded him to go to Pharaoh. The Prophet Muhammad (peace be upon him) encouraged supplicating with Quranic duas as they are the words of Allah Himself.