Answered by Shaykh Muhammad ibn Adam al-Kawthari
Is it permissible for a Muslim to send delinquent clients without standing accounts to a collection agency when it is possible that the said agency will charge interest to the individual if they do not pay within a certain time? Not all of the clients will be charged interest, but some of them will.
In the name of Allah, the Compassionate, the Merciful.
When you send a Muslim to the mentioned collection agency and you are confident that he will not default and will pay his bill before any interest becomes due and also that his habit and past experience shows that he will pay in time, then it will be permissible to refer him to the said agency.
If however, you are aware that he will not pay his bill in time and thus be involved in interest, then it will not be permissible. If there is no knowledge of his past experience and you do not incline towards any direction, then it is better not to send the Muslim to the agency. However, it would be permissible.
This ruling is based on the concept of being a cause for somebody else’s sin. Imam al-Shatibi (Allah have mercy on him) mentions this in detail in his famous treatise al-Muwafaqat.
Ibn Abideen (Allah have mercy on him) says in his “Hashiya”: If you are the the main cause for a sin [meaning if the cause would not have been there, then there was no reason for him to sin] it will be Haraam, otherwise it will be Makrooh.
And Allah knows best.
Muhammad ibn Adam al-Kawthari, UK