Nowhere. I didn't say that you did. Did you just speed read through people's posts or something? How is it that you so often misunderstand what people are saying?
You need to be more clear when you say things like this. They did not knowingly and purposely prophesy of two comings of Christ. Is that what you mean? Surely, the day of the Lord that Joel prophesied in relation to being "great and very terrible" (Joel 2:11) correlates with the future day of the Lord when Christ returns and that will result in great and very terrible wrath upon unbelievers, as Paul and Peter wrote about, right? But, it's not specified thYere that it's referring to something in relation to the second coming of Christ. The second coming of Christ is never explicitly referred to in the Old Testament. If that's what you're saying, then I agree. But, certainly, things that we now know are related to what will happen when He comes again are written about in the Old Testament, like the resurrection of the dead and the judgment and the ushering in of the new heavens and new earth.
Because you seemed to be talking about people believing in two future comings of the Lord, as they believe. You're not being clear in what you're saying. You didn't make it clear that the OT doesn't explicitly prophesy of two comings of Christ. I would agree with that. But, it does prophesy of things that will occur at His second coming without explicitly indicating that those things would occur as part of His second coming.