On August 22, 2006, the ICM awarded Perelman the Fields Medal for his work on the Ricci flow, but Perelman refused the medal.

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The Clay Mathematics Institute, having included the Poincaré conjecture in their well-known Millennium Prize Problem list, offered Perelman their prize of US$1 million in 2010 for the conjecture's resolution. He declined the award, saying that Hamilton's contribution had been equal to his own

https://arxiv.org/abs/math/0211159

https://en.wikipedia.org/wiki/Grigori_Perelman

https://en.wikipedia.org/wiki/Richard_S._Hamilton

https://en.wikipedia.org/wiki/Ricci_flow

https://en.wikipedia.org/wiki/Millennium_Prize_Problems

Note: the possible second Millennium Prize Problem solution (Navier–Stokes, possibly solved recently) has still not yet been verified by CMI.