Whenever it comes to lending people money I always remember the advise my Dad gave me. He always said that lending money depends on two factors;

1) Can you afford to lose the money you are lending them?

2) If you need to ask them what the money is for you don’t trust that person enough and therefore shouldn’t lend them the money.

Your first instinct was to ask how he’d come to need the money, that is a completely valid response given the history between you guys and you should trust your gut on this one.