Is it my taxable income if my debtor repays the debt to me?

Did you deduct what "you" paid from your taxable income? If yes, then what you were reimbursed is reportable taxable income. If no, then do nothing.

I don't understand...you paid someone's bill, and they paid you back...there's no income or deductions involved in that transaction...why would you need to prove anything to anyone?

Lisa, as an example, if it's rental property, then "all" income received in that capacity is reported as rental income. So if the rent is say, $1000/mo and includes an allowance of say, $200/mo for utilities paid by the landlord, if the renter pays the landlord for excess utility use, the landlord counts that excess as part of the rent received, and it's taxable.
Then the landlord could claim the total amount paid for utilities, as a tax deductible rental expense. That's but one possible scenario where this stuff comes into play.

Nothing was mentioned about rentals.  And he is using the Free Edition.  I agree with Lisa, why do you need to prove anything?  Doesn't sound like anything that needs to go on a tax return.    We  would need to know more details about it..

Thank you for your responses.
Let me give you an example. Imagine I'm a bad guy. Imagine I made some work or service to someone and he paid me $1000 for my service via checking-to-checking transfer. Then I bought something on Amazon online for the same $1000 using my credit card. After that I can say to IRS that I bought this thing on Amazon for that person (not for myself) and the person just reimbursed my expenses. So it's potentially a way how to avoid paying taxes. So should I prove to IRS that I'm not a tricky guy? In case of random audit they would see some transfer from someone to my checking account and it would not be clear the nature of this transfer.

So in this situation (of audit) IRS would need to prove that I'm a liar or I would need to prove that I'm honest? At least could they require some explanations from me in writing about the nature of this money I received?

So how would they separate good guys from bad guys?

P.S. to the 1st Carl's message. I'm not planning to fill up the amount that I paid with my credit card into any IRS form (so obviously I'm not going to ask for tax deduction) -- if I understood you correctly

And for more details, I helped them several times. I paid utilities bills, purchased things on Amazon and some show tickets -- totally maybe $2-3K. And later this person returned me my money (checking acc to checking acc transfer).

If I loan you $10,000 for any period of time, (days, weeks, decades, it doesn't matter) I do not report that loan to the IRS or state taxing authorities for any reason. There is no reason to. Therefore, I the lender (not you) pay taxes on that money. It's my money, not your's, so you don't report it to any taxing authority either.
When you pay me back, you are paying me *MY* money that I already paid taxes on. I have no taxable income to report. You are paying me money that was never yours, and *YOU* never paid taxes on. So *YOU* have nothing to claim or report either.

Hi Carl,
Thank you for your response.
So the bottom line. In case of IRS audit they could wonder the nature of the money that people transferred to me. They could request the explanation. I would present them 1) my credit card statement, 2) my checking account statement, 3) as well as my explanation that this money was just reimbursement of my expenses helping to my friends.

(Once again, it's totally not clear out of my credit card statement *WHO BENEFITED FROM THESE PURCHASES* -- me or 3rd party. And I guess this is the biggest potential problem.)

And they MUST believe me and my explanations (unless they prove that I've lied) that I made these purchases for someone else (not for me).
Is this correct?
Is this how it normally works here in the USA?

So this is not a theoretical tax law question, it's more about how it would work in practice -- how IRS employees would treat this situation and how they would consider it. Because you know sometimes your fair behavior could look suspicious as well as your unlawful behavior could look lawful.

Thank you

You're making mountains out of molehills. Don't worry about it. I seriously doubt anyone at the IRS is scrutinizing your return, of the over 300,000,000 million returns they receive each year. More than 90% of those filed returns are never seen by human eyes. The 10% that are, are those kicked out by the computers.
Even the returns that are printed and mailed get scanned into their computers. Rarely does a human actually read one and scrutinize it.
They have a system that will radnomly kick out returns based on programmed criteria for human review, as a rough "checks and balances" thingy, and that's it. One year, they paid attention to charitable donations. Another year, they paid attention to home energy credits. So your chances of being targeted are about the same as mine are - which is nil.

@yshpakov The fact that you are so worried about this leads me to believe that something else is going on, and that maybe you should not even do this.