رَبِّ اشْرَحْ لِي صَدْرِي وَيَسِّرْ لِي أَمْرِي وَاحْلُلْ عُقْدَةً مِنْ لِسَانِي يَفْقَهُوا قَوْلِي
Rabish rahli sadri wa yassir li amri wahlul 'uqdatam min lisaani, yafqahu qauli
My Lord, expand (i.e. relax) for me my breast (with assurance) and ease for me my task and untie the knot from my tongue that they may understand my speech.
[Surah Taha Verse 25-28]
This dua is usually recited to help you cure stammers/stuttering or for success.
This beautiful dua was originated and used when Prophet Musa asked Allah's help to ease his missions of da'wah, and release the knot in his tongue so they all can understand the message of Allah SWT.
By reciting the dua, InshaAllah when at times where we're expected to be courageous, it will help us to speak up with confidence. InshaAllah the dua will help us to get through the issues that lies ahead and make it easier than it is expected to be.
Making the dua as a habit are mentioned in the Quran and Mashallah for us to be reciting something positive and that is the dua that is uttered by the Prophet, thousand years ago.