Ibrãhim bin Muhammad bin Sa’d narrated from his father, from Sa’d, that the Messenger of Allah (Sallallāhu alayhi wa sallam) said:

“The supplication of Dhun-Nun [Prophet Yunus (as)] when he supplicated, while in the belly of the whale was:

لَّا إِلَهَ إِلَّا أَنتَ سُبْحَانَكَ إِنِّي كُنتُ مِنَ الظَّالِمِينَ

La Ilãha lila Anta Subhanaka Inni Kuntu Minazalimin
‘There is none worthy of worship except You, Glory to You. Indeed, I have been of the transgressors.’

So indeed, no Muslim man supplicates with it for anything, ever, except Allah responds to him.”

[ Tirmidhi 3505 – Sahih ]

This is a supplication in the Quran, which was asked by Yunus (as) inside the belly of the whale in Surah Al-Anbiya (21) verses 87 and 88 as follows:

And remember Dhu al Nun, when he departed in wrath: he imagined that We had no power over him! but he cried through the depths of darkness “There is no god but Thou: Glory to Thee: I was indeed wrong!” (87) So We listened to him: and delivered him from distress: and thus do We deliver those who have faith. (88)