Dealing with Riba-based Banks
1-8-2022 | IslamWeb
Question:
My brother works as a Valuer. Some interest based banks refer to him for valuation of some properties like land or a house. Based on his report of valuation of the said properties the banks decide on giving loans etc to their customers. For the valuation the banks pay certain amount as fees to him. Is this income Halal according to Sharia.. Or will it be considered as assisting in usery.
Answer:
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.
It is not permissible for your brother to deal with Riba-based banks as a valuer or anything else, because this is helping the bank in its Riba-based transactions.
You mentioned in the question, that it is based on your brother's report of valuation on the properties (or land) that the banks decide on giving loans etc to their customers. This is a clear help, so your brother must fear Allah and stop this forbidden help.
Jaabir 
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]
The curse was not limited to the one who consumes it, or who gives it to others to consume it; rather, it included the one who helps in it.
What he earns from a forbidden job is ill-gotten and evil money and he is not permitted to benefit from it; rather, he must dispose of it unless he is ignorant of the prohibition of that work in the past. In which case, he may benefit of what he earned from it prior to his knowledge of the prohibition according to the view of some scholars.
Shaykh Ibn 'Uthaymeen 
said:
“If he had taken it, then if he was ignorant of it and did not know that it is forbidden, then his repentance wipes out his previous sins, and he may take it, because Allah says (what means): {So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allah.} [Quran 2:275]
But if he took it while he knew that it was forbidden, but he was weak in the religion, and had little insight, then he must gift it in charity. If he wishes he may gift it on building mosques, or in repaying debts of those who are unable to repay, or in spending it on his needy relatives, as all this are acts of goodness.”
Allah knows best.