Is it permissible to ascertain the value of usurious interest and deduct it from other funds after withdrawing the entire amount and building a house with it?

It is necessary to know the amount of usurious interest or to be cautious in this regard and to extract it from any money; because it is not related to the money itself, but to the liability of the one who took it. Ibn Taymiyyah said: "If unlawfully acquired money is mixed with lawful money, then what is obligatory is to extract that unlawful amount from it." Ibn al-Arabi said: "If the matter becomes ambiguous and one does not know how much of the unlawful is mixed with the lawful, then one should estimate the amount that must be returned until what remains becomes pure for him." A Muslim is also required to avoid doubtful matters.