It's not a problem. Tell him you will pay the land owner in 6 weeks. I'm looking forward to hear the answer that you'll get. Probably they'll need the money faster than that because the land owner's little daughter needs a kidney transplant.
No seriously, it is of course a scam, and a classical one. This one comes in many, many variations, but it is always the same thing.
- You get money because <insert plausible reason>.
- You are asked to somehow forward it to an accomplice (Nigerian prince, distant heir, aunt, land owner)
- You do so.
At (4) you notice that the original payment has meanwhile been revoked. For... whatever reason, and by whatever means. Only just, now it's too late because you already did (3). So, the other guy just magically doubled his money, and you, well... didn't make as much profit as you hoped for. The Prince won't answer your phone calls and the land owner turns out being not the land owner at all.
Thus, the only reasonable (or half-reasonable) things to do are to either not do anything at all (and inform police), or wait 6 weeks, and confirm that the money is still on your account before proceeding.
However, even after letting 6 weeks pass, it's doubtful whether you really want to do it because you cannot be sure you aren't aiding and abetting in money laundry. I mean, do you really want to risk 10 years of prison for a 100 dollar tip?
Another thing to consider just occurred to me, too, which might be worth yet another consideration. You stated in some comment that you received the money not personally, but via quickbook. Which means that the 12k that you have received is, by all legal means, income for which you have to pay tax!
Sure enough, with a little luck nobody will notice. But chances are that you get an audit, and these 12k that very clearly are income do not appear in your books, nor did you ever pay tax for them. That's bad, very bad, even for the vain chance that this isn't a scam.
But worse, imagine that after falling for a scam and losing 12k, you have to pay tax and a penalty... for a 12k income that you've never had.