Wiz Khalifa held on to newborn son Sebastian Taylor Thomaz ... his baby with Amber Rose.

The 29-year-old new mom Tweeted the above photo with the following: "Best daddy ever. Up with the baby so Muva can go back to sleep."

Sebastian was born Thursday. Wiz and Amber have nicknamed their little boy "The Bash."

The couple got engaged in March 2012. Perhaps wedding bells are in the near future now that their little bundle has arrived.