Sponge baths are fine as well, but it's still advisable that you use a washcloth to wipe his body as well.
The thing about using a sponge instead of a washcloth is that sponges are excellent breeding grounds for bacteria and germs, so be sure to change the sponges frequently.
http://www.drugstore.com/baby-buddy-natural-bath-sponge-yellow/qxp503283
http://www.babycenter.in/x1015318/how-do-i-give-my-baby-a-sponge-bath