When one is in debt, one should recite the following dua:
اَللّٰهُمَّ اكْفِنِي بِحَلَالِكَ عَنْ حَرَامِكَ، وَأَغْنِنِي بِفَضْلِكَ عَمَّنْ سِوَاكَ
O Allah! Suffice me with Your halal from Your haram (i.e. suffice me with sustenance and wealth which You have declared as halal and save me from sustenance and wealth which You have declared as haram), and through Your special grace, make me independent from everyone besides You.
عن علي أن مكاتبا جاءه فقال: إني قد عجزت عن مكاتبتي فأعني، قال: ألا أعلمك كلمات علمنيهن رسول الله صلى الله عليه وسلم لو كان عليك مثل جبل صير دينا أداه الله عنك، قال: قل: اللهم اكفني بحلالك عن حرامك، وأغنني بفضلك عمن سواك (سنن الترمذي الرقم: 3563)
Hazrat Ali رضي الله عنه reports that on one occasion, a mukaatab slave (a slave who enters into a contract with his master that upon paying a certain amount, he will receive his freedom) came to him (seeking assistance). He addressed Hazrat Ali رضي الله عنه and said, “I am unable to pay the amount for my freedom, so (if you are able to assist me then) assist me.” (At that time, perhaps Hazrat Ali رضي الله عنه did not possess any wealth. Therefore, he did not offer him any financial assistance.) Hazrat Ali رضي الله عنه responded saying, “Shall I not teach you some words (of dua) which Rasulullah صلي الله عليه وسلم had taught me? These words are such that even if you have so many debts which equal Mount Seer (the name of a certain mountain), Allah Ta‘ala will settle all your debts for you?” Hazrat Ali رضي الله عنه then taught him the following dua:
اَللّٰهُمَّ اكْفِنِيْ بِحَلَالِكَ عَنْ حَرَامِكَ وَأَغْنِنِيْ بِفَضْلِكَ عَمَّنْ سِوَاكَ
(ihyaauddeen.co.za)