On his website, John Piper says
When I read about prosperity-preaching churches, my response is: “If I were not on the inside of Christianity, I wouldn’t want in.” In other words, if this is the message of Jesus, no thank you.
Luring people to Christ to get rich is both deceitful and deadly. It’s deceitful because when Jesus himself called us, he said things like: “Any one of you who does not renounce all that he has cannot be my disciple” (Luke 14:33). And it’s deadly because the desire to be rich plunges “people into ruin and destruction” (1 Timothy 6:9). – Source: Prosperity Preaching: Deceitful and Deadly
In a video titled, “Why I abominate the prosperity gospel,” John Piper further explains his views on the prosperity gospel:
See also: “Is it ever appropriate to call out prosperity gospel teachers by name?”
Who is John Piper?
John Piper is pastor for preaching and vision at Bethlehem Baptist Church in the Twin Cities of Minnesota. He grew up in Greenville, South Carolina, and studied at Wheaton College, Fuller Theological Seminary (B.D.), and the University of Munich (D.theol.). For six years he taught Biblical Studies at Bethel College in St. Paul, Minnesota, and in 1980 accepted the call to serve as pastor at Bethlehem. John is the author of more than 40 books and more than 30 years of his preaching and teaching is available free at desiringGod.org. John and his wife, Noel, have four sons, one daughter, and twelve grandchildren.
– Source: Who is John Piper, DesiringGod — God-centered resources from the ministry of John Piper
Additional information about John Piper is available at that link.
Our research resources page on the prosperity gospel includes links to articles on the subject by John Piper