Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
I have a harsh tongue. What can I do to remedy this?
You must remember the consequences of what you say in the next life and reflect on what has been narrated about guarding the tongue in the Sunnah.
Repeat this du`a in abundance:
اللَّهُمَّ اهْدِ قَلْبِي و سَدِّدْ لِسَاني
Allahumma’hdi qalbi wa saddid lisani
O Allah, guide my heart and set right my tongue
Also repeat this verse 100 times a day:
هُوَ اللهُ الَّذي لا إِلهَ إِلا هو عَالِمُ الغَيْبِ والشَّهادَةِ هُوَ الرَّحْمَنُ الرَّحِيم
HuAllahu’lladhi la ilaha illa hu, ‘Alimu’l ghaybi wash-shahada, Hu arrahmanu’ rahim
He is Allah, there is no god other than Him, knower of the unseen and the seen, He is the All-Compassionate, the All-Merciful. (Al-Hashr, 59:22)