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 halaal from Your haraam (i.e. suffice me with sustenance and wealth which You have declared as halaal and save me from sustenance and wealth which You have declared as haraam), 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 (radhiyallahu ‘anhu) 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 (radhiyallahu ‘anhu) 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 (radhiyallahu ‘anhu) did not possess any wealth. Therefore, he did not offer him any financial assistance.)
Hazrat Ali (radhiyallahu ‘anhu) responded saying, “Shall I not teach you some words (of dua) which Rasulullah (sallallahu ‘alaihi wasallam) 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 (radhiyallahu ‘anhu) then taught him the following dua:
اَللّٰهُمَّ اكْفِنِيْ بِحَلَالِكَ عَنْ حَرَامِكَ وَأَغْنِنِيْ بِفَضْلِكَ عَمَّنْ سِوَاكَ