MIAMI (AP) -- Ricky Williams has told the Miami Dolphins that he's retiring after just five years in the NFL, The Miami Herald reported on its Web site Sunday.

Williams said he was overjoyed by his decision.

"You can't understand how free I feel,'' Williams told the Herald in a cell phone interview Saturday before boarding a plane in Hawaii and heading to Asia to begin several months of travel.

The 27-year-old running back, who started his career with the New Orleans Saints, said he plans to file his retirement papers with the NFL on Monday or Tuesday.

Williams told Dolphins coach Dave Wannstedt of his decision Friday and said Wannstedt tried to persuade him to reconsider. Miami opens training camp Friday.

The Dolphins acquired Williams from New Orleans for two first-round draft picks in 2002, and he led the NFL in rushing that year.

Phone messages left early Sunday with two Dolphins officials and Williams' agent, Leigh Steinberg, weren't immediately returned.

"I have no comment,'' Wannstedt told the Herald when asked about Williams' retiring. ``Players report Friday. Right now, it's a 10-day dead period. We'll get everybody started on Friday.''

Wannstedt acknowledged talking with Williams but declined to give details of their conversation.

Williams said there was no chance he would change his mind.

He said he has already told his mother Sandy, Steinberg, backup running back Travis Minor and friends and family of his decision.

In May, three South Florida newspapers reported that Williams tested positive for marijuana and faced a fine of at least $650,000 for violating the league's substance-abuse policy for a second time since joining the Dolphins.

But his attorney, Gary Ostrow, told The Associated Press: ``As far as I'm concerned, there is no violation.''

Williams told the Herald his failed marijuana tests had a minor influence on his decision to retire, but was only one of many factors. It didn't cause him to retire, he said, as much as reinforce his reasons for wanting to do so.

Williams' two seasons with the Dolphins have been the best of his career. He set a team record with 1,853 yards rushing in 2002. He followed that with 1,372 yards last season.