All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
With regard to the first person who borrowed the price of the house with Riba (interest and usury), then he has indeed made a great mistake and committed a grave major sin because Riba is among the greatest sins and the most abominable acts of disobedience and it is not permissible to resort to it except in case of dire necessity that permits a person to commit what is forbidden as clarified in Fataawa 100833, 86371 and 133941.
A person who can afford a house even by renting is not in necessity to borrow money with Riba. However, since this person has repented from his sin and regretted having done it, then we hope that this will be accepted from him and he is not obliged to sell the house which he purchased with the Riba-based loan as the sin of Riba is related to the person who took it and not to what the loan was spent on. So, he may sell it and benefit from its price. Anyway, he should be grateful to Allaah Who enabled him to repent with His Mercy and Grace before death comes to him while he is heedless.
As regards the second person who refused to deal with Riba, and he did not want to own the house except by a legitimate means, then he has indeed done well, and this is what he is Islamically required to do and he will be greatly rewarded for it and Allaah will compensate him with something better as whoever leaves something for the Sake of Allaah, Allaah will compensate him with something better. So, he should not regret having done this good act.
Finally, it should be mentioned that some people may be lured by the devil who whispers to them to commit what is forbidden with the intention of repenting from it afterwards, but who knows that he would fulfill what he intends to do. Indeed, not every sinful person is enabled to repent from his sin; rather, his heart could be sealed because of daring to commit this sin.
We ask Allaah to grant us safety from sin.
Allaah Knows best.