A wealthy Zimbabwean entrepreneur known for fighting corruption said he was solicited for bribes by government officials, the private sector and even presidents as he built his businesses in Africa, the WashingtonPost reports.

On a social network posting that went viral Monday, Strive Masiyiwa said his weapon against corruption was the word “no.” The 53-year-old devout Christian and member of former U.S. President Bill Clinton’s African charity said he never paid a bribe.

Masiyiwa’s Econet Wireless conglomerate and group of telecommunications companies operates in more than 15 African countries. He also helped pioneer a mobile phone banking system in impoverished African regions where money can be transferred in small amounts through a messaging service.

Masiyiwa first rose to prominence in Zimbabwe after a five-year court battle against the state telephone monopoly that he won in 1998, opening Zimbabwe’s mobile phone market to private commercial competitors for the first time.

Now one of Zimbabwe’s wealthiest businessmen, the anti-corruption campaigner said he has been “viciously persecuted” for his views.

“Some of the worst corruption I have witnessed was not in governments but in the private sector. Some of the most corrupt people I have known were not Africans but we as Africans must take responsibility, individually and collectively, to fight corruption,” said Masiyiwa.

The Associated Press reports that two politicians demanded a bribe from Masiyiwa of $8 million to keep one contract in a country where his Econet Wireless conglomerate earned $30 million a year. “I refused,” he said, not naming the country. “We were thrown out.”

A president in another country asked for an offshore bribe as he “needed something in retirement,” Masiyiwa said, adding that he was invited to the state palace where he was asked to “quietly accommodate” the president.

“We have yet to return to that country but we will one day,” he said in a series of Facebook and Twitter postings over the weekend.

Another president’s son asked for a 20 percent payout on a multimillion-dollar investment deal, he said.

“I withdrew our bid. I had no regrets,” he said. That ruler and his family lost an election and “we returned to that country and are doing very well.”

Masiyiwa’s efforts led to convictions in some cases, he said. In one case, he said a large contract went to one of his firm’s largest global competitors listed on the New York Stock Exchange.

“I reported them to the U.S. Justice Department. They admitted their officials had paid the bribes and fired the officials,” he said.

One of the corrupt politicians ended up in jail, he said.