بسم الله الرحمن الرحيم
Islam has set some commandments in Shari’ah which are related to Allah such as salah, fast, zakah and other worships etc, and some commandments are related to the creatures like (dealings, social life, morals etc) for example, obeying and respecting one’s parents, taking care of one’s wife and children, behaving one’s neighbours well, keeping dealings transparent; and paying the debt of a person on time also includes this. It is injustice to make unnecessary delay [in the payment of debt]. It is recorded in one Hadith:
مطل الغني ظلم .
[Translation: Delay (in the payment of debt) on the part of a rich man is injustice.]
And if a person has given someone a debt then he should grant him time to pay the debt at his convenience, as giving more time is cause of forgiveness, which is known by a narration of Bukhari. The person who practices these two types of commandments is true Muslim. If someone acts upon one type of commandment and ignores the other one then he cannot be true believer in the sight of Shariah. Hence it is mandatory that the person in the question is made understood with wisdom and he is apprised of the warnings which are found for those who make a delay in paying the debt or not paying a debt. It is possible that he receives taufiq from Allah to follow it.
ادْعُ إِلِى سَبِيلِ رَبِّكَ بِالْحِكْمَةِ وَالْمَوْعِظَةِ الْحَسَنَةِ وَجَادِلْهُم بِالَّتِي هِيَ أَحْسَنُ إِنَّ رَبَّكَ هُوَ أَعْلَمُ بِمَن ضَلَّ عَن سَبِيلِهِ وَهُوَ أَعْلَمُ بِالْمُهْتَدِينَ [النحل : 125]
[Translation: Invite (people) to the way of your Lord with wisdom and good counsel. And argue with them in the best of manners. Surely, your Lord knows best the one who deviates from His way, and He knows best the ones who are on the right path].
Allah knows Best!
Darul Uloom Deoband