It is reported that on one occasion, a mukaatab slave came to Hazrat Ali (radhiyallahu ‘anhu) seeking assistance. A mukaatab slave is a slave who enters into a contract with his master that upon paying a certain amount, he will receive his freedom.
The mukaatab slave 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. Rather, he responded saying, “Shall I not teach you some words (of du‘aa) which Rasulullah (sallallahu ‘alaihi wasallam) taught to me? These words are such that even if the debt upon you is as great as the Mountain of Seer (the name of a certain mountain), Allah Ta‘ala will still settle the debt for you?”
Hazrat Ali (radhiyallahu ‘anhu) then taught him the following du‘aa:
اَللّٰهُمَّ اكْفِنِيْ بِحَلَالِكَ عَنْ حَرَامِكَ وَأَغْنِنِيْ 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.
(Sunan Tirmizi #3563)