Sa’d reported: The Messenger of Allah, peace and blessings be upon him, said, “The supplication of Jonah, Dhul Nun, when he called upon Allah inside the belly of the whale was this, ‘There is no God but You, glory be to You for I have certainly been among the wrongdoers,’ (21:87). Verily, a Muslim never supplicates for anything with it but that Allah will answer him.”
Source: Sunan al-Tirmidhī 3505
Grade: Sahih (authentic) according to Al-Albani
عَنْ سَعْدٍ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ دَعْوَةُ ذِي النُّونِ إِذْ دَعَا وَهُوَ فِي بَطْنِ الْحُوتِ لَا إِلَهَ إِلَّا أَنْتَ سُبْحَانَكَ إِنِّي كُنْتُ مِنْ الظَّالِمِينَ فَإِنَّهُ لَمْ يَدْعُ بِهَا رَجُلٌ مُسْلِمٌ فِي شَيْءٍ قَطُّ إِلَّا اسْتَجَابَ اللَّهُ لَهُ
3505 سنن الترمذي أبواب الدعوات
المحدث الألباني خلاصة حكم المحدث صحيح في صحيح الترغيب 1826