This is one of the greatest duas we can make and that is for Allah to protect our Imaan. After Allah has shown us the true path we need to make dua to stay on it.
This dua is from the following hadith narrated by Asma’: The Prophet said, I will be at my Lake-Fount (Kauthar) waiting for whoever will come to me.Then some people will be taken away from me whereupon I will say, ‘My followers!’ It will be said, ‘You do not know they turned Apostates as renegades (deserted their religion).’ (Ibn Abi Mulaika said, Allah, we seek refuge with You from turning on our heels from the (Islamic) religion and from being put to trial )
اللّٰهُمَّ إِنَّا نَعُوذُ بِكَ أَنْ نَّرْجِعَ عَلَى أَعْقَابِنَا أَوْ نُفْتَنَ.
Ya Allah, we seek refuge with You from turning on our heels from the (Islamic) religion and from being put to trial