Soulja Boy was arrested early this morning for weed possession ... and law enforcement sources tell TMZ cops allegedly found a ton of weed and cash during the arrest.

The 21-year-old rapper -- real name DeAndre Cortez Way -- was popped early this morning by Temple Police Department officers in Temple, GA at 3:15 AM.

Law enforcement sources tell TMZ ... Soulja was riding in an Escalade with 4 other men, which was originally pulled over for a traffic violation.

We're told ... during the stop, cops found a "substantial amount" of marijuana and cash inside the vehicle." Soulja and the 4 other men were all arrested. Soulja is still being held in Carrol County Jail.

Law enforcement sources tell us officers also found guns inside the car -- though it's unclear if any of the men had the proper licenses to be in possession of the firearms. We're told an investigation is underway.

One source with knowledge of the situation tells us there was roughly $70,000 in cash and drugs in the car.

9:05 AM: Law enforcement tells TMZ, all 5 men were arrested on charges of possession of marijuana, possession with intent to distribute, and possession of a firearm during the commission of a crime.