What is the ruling on taking a loan from a person whose money is from haram, or about which you suspect it is from haram?

There is a difference between someone who knows their money is unlawful (haram) and someone who merely suspects their money. For one whose money is known to be unlawful, dealing with them is impermissible. However, for one whose money is merely suspected, there is no harm in dealing with them or borrowing from them. If it is known that a person has stolen money or usurped it, then it is impermissible to take money from them in any way, because it is the money of the oppressed. But if the status of the money is unknown, the default is that it belongs to its owner unless proven otherwise, and there is no harm in dealing with them. However, if it is known that the person deals in unlawful matters, then it is advisable to avoid dealing with them as a matter of piety. As for someone whose financial situation is undisclosed, there is no doubt in dealing with them.