While there are no IRS rules that specifically forbid you from depositing your refund into someone else's account, we don't recommend it.
Why not? Because most banks have fraud-prevention measures that won't allow a direct deposit into an account bearing a different name.
If you decide to enter someone else's account information anyway, chances are the bank will reject the IRS's direct-deposit request because the name on the refund (yours) doesn't match the account holder's.
The IRS will then have to re-process the refund, cut a check, and send it by mail. You will (eventually) get your refund, but it'll take longer than it would have taken had you requested a check refund in the first place.
You can also contact your financial institution or visit their website for the routing number. If they have multiple routing numbers to choose from, get the electronic direct deposit routing number, and your account information.