Ali (May Allah be pleased with him) reported: A slave who had made a contract with his master to pay for his freedom, came to me and said: “I am unable to fulfill my obligation, so help me.” He said to him: “Shall I not teach you a supplication which the Messenger of Allah (ﷺ) taught me? It will surely prove so effective that if you have a debt as large as a huge mountain, Allah will surely pay it for you. Say:

اللَّهُمَّ اكْفِنِي بِحَلاَلِكَ عَنْ حَرَامِكَ وَأَغْنِنِي بِفَضْلِكَ عَمَّنْ سِوَاكَ

‘Allahumm-akfini bihalalika ‘an haramika, wa aghnini bifadlika ‘amman siwaka (O Allah! Grant me enough of what You make lawful so that I may dispense with what You make unlawful, and enable me by Your Grace to dispense with all but You).”
Jami` at-Tirmidhi 3563 Vol. 6, Book 46, Hadith 3563

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ عَبْدِ الرَّحْمَنِ، أَخْبَرَنَا يَحْيَى بْنُ حَسَّانَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ إِسْحَاقَ، عَنْ سَيَّارٍ، عَنْ أَبِي وَائِلٍ، عَنْ عَلِيٍّ، رضى الله عنه أَنَّ مُكَاتَبًا، جَاءَهُ فَقَالَ إِنِّي قَدْ عَجَزْتُ عَنْ كِتَابَتِي فَأَعِنِّي ‏.‏ قَالَ أَلاَ أُعَلِّمُكَ كَلِمَاتٍ عَلَّمَنِيهِنَّ رَسُولُ اللَّهِ صلى الله عليه وسلم لَوْ كَانَ عَلَيْكَ مِثْلُ جَبَلِ صِيرٍ دَيْنًا أَدَّاهُ اللَّهُ عَنْكَ قَالَ ‏ “‏ قُلِ اللَّهُمَّ اكْفِنِي بِحَلاَلِكَ عَنْ حَرَامِكَ وَأَغْنِنِي بِفَضْلِكَ عَمَّنْ سِوَاكَ ‏”‏ ‏.‏ قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ ‏.‏