Tens of thousands of people took to the streets of Kuala Lumpur, the capital of Malaysia, on Saturday to call for the resignation of Prime Minister Najib Razak, who is accused of taking $1 billion from a government investment fund.

The protesters, wearing the yellow T-shirts of Malaysia’s clean government movement, known as Bersih, converged on the city center to hear their leaders call for Mr. Najib’s ouster. Among the speakers was former Prime Minister Mahathir Mohamad, 91, who once chose Mr. Najib as prime minister but now criticizes his former protégé’s government as corrupt.