the power of sincere supplication (du'a)

وَذَا ٱلنُّونِ إِذ ذَّهَبَ مُغَـٰضِبًا فَظَنَّ أَن لَّن نَّقْدِرَ عَلَيْهِ فَنَادَىٰ فِى ٱلظُّلُمَـٰتِ أَن لَّآ إِلَـٰهَ إِلَّآ أَنتَ سُبْحَـٰنَكَ إِنِّى كُنتُ مِنَ ٱلظَّـٰلِمِينَ

And [mention] the man of the fish [i.e., Jonah], when he went off in anger and thought that We would not decree [anything] upon him. And he called out within the darknesses, "There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers."