B.B.
He's four. Lying in a four year-old is not the same as lying in an older child or adult. He doesn't really get the concept of lying at this point, he's not trying to misbehave.
Here is an short article about the topic, and you may find it useful to do some more research on development at this age to help you decide how to proceed.
In the interest of honesty, a four year-old getting spanked for dishonesty makes me cringe.
http://www.babycenter.com/0_lying-why-it-happens-and-what...