He made the announcement at a private meeting with around 1000 Evangelical pastors at a hotel in Times Square, New York.
Members of the new group include former Minnesota congresswoman Michele Bachmann, Liberty University president Jerry Falwell Jr and Faith and Freedom Coalition leader Ralph Reed.
Bishop EW Jackson, who was also at the conference, posted videos of it on Twitter:
Donald Trump said at the meeting: "Christianity, I owe so much to it in so many ways, through life, through having incredible children, through so many other things.
"You can pray for your leaders, and I agree with that, pray for everyone. But what you really have to do is you have to pray to get everybody out to vote for one specific person.
"And we can't be again politically correct and say we pray for all of our leaders because all of your leaders are selling Christianity down the tubes, selling evangelicals down the tubes."
Mr Trump also spoke of the support he had from Christians, and the need for spiritual revival in America: "The evangelical vote was mostly gotten by me.
"We've got to spiritise (sic) this country.
"And I'm not only talking about the inner cities. I'm talking about everywhere."