Should he sell lend to one who he knows will use it as collateral for a riba-based loan?

No File Exists
Check below answers in case you are looking for other related questions:
Prohibition on selling dogs
Can he sell computer programs even though he is afraid that they may be used for haraam purposes?

No File Exists
Related Answers:
What is the ruling on selling his share in a company whose wealth is all debts that are owed by people?
Selling a box of toys whose contents are unknown
He buys gold over the phone then it is sent to him
Prohibition on selling dogs
Can he sell computer programs even though he is afraid that they may be used for haraam purposes?

Recommended answers for you:
Ruling on wife taking the husband’s last name if the husband insists on that
Will children who die young go to Paradise or Hell?
Reading Soorat al-Mulk protects one from the torment of the grave
Ruling on photographs
Ruling on smoking the argileh or shisha – and a discussion on its harmful effects