All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Borrowing money with Riba (Interest/Usury), is one of the major prohibitions; so, it is not permissible to help a person by guiding him to it or writing it (this contract of Riba).
Jabir narrated that the Prophet said “Allah has cursed the one who consumes Riba (i.e. usury or interest), the one who gives it to others, the one who records it and the one who witnesses it (its transaction).” He added: “All of them are equal in sin.” [Muslim]
An-Nawawi said in Sharhf Muslim:
“This is an explicit statement on the prohibition of recording sale transactions between two parties in a Riba-based contract or being a witness on them. It also proves the prohibition of helping in falsehood.” [End of quote]
As for selling real estate to someone who buys it with money borrowed with interest; there is nothing wrong with it, because we are of the view that the prohibition of interest-based loans is related to the borrower who borrowed money with Riba and not to the very money.
If there are any developers who lend goodly loan [a loan without Riba], then there is nothing wrong with guiding people to these loans and helping them with it.
For more benefit on the prohibition of borrowing money with Riba and the ruling of dealing with Riba, please refer to Fatawa 404938, 402904, 100833, 379279, 136065, 86136 and 86521.
Allah Knows best.