يَا مُقَلِّبَ الْقُلُوبِ ثَبِّتْ قَلْبِي عَلَى دِينِكَ
Transliteration
Ya Muqallibal-qulubi thabbit qalbi 'ala dinik
English meaning
O Turner of hearts, make my heart firm upon Your religion.
When is it recited?
Recommended to be recited frequently.
Its virtue
The Prophet (PBUH) used to recite this supplication very frequently.
Source
Tirmidhi, Da'awat 89, 3522; Ahmad, 6/294