As someone who has supplied “gift” money for downpayments to several relatives already I highly recommend seasoning if you want to cut down on the potential hassle factor. Sure you can sign a gift letter but the gifter has to sign paper work too and if the “gift” is large they are inclined to call the gifter to make sure it is really a “gift” and not a loan you are expected to pay back and thus increase your debt load. With lenders ultra cautious these days who knows what they will do. Properly season and you won’t have to deal with pesky questions.