You can simply transfer the money as usual (wire transfer, or any other means). There are no tax implications for moving money into and out of the US, and nobody will care (unless you transport it in cash).
The tax implications are from having that home in the first place. You are required to report on your tax filings all income and property outside the US, although it is of course possible that the house produced no income for you.
If the house was owned by your mom, and she is gifting you the amount now, this is a taxable gift, which she - not you - has a US tax liability for, if she is a US person (and independantly, potentially a tax liability in her home country, which you didn't name).
For a mother-to-son gift, the US tax exclusion is 15000 per year; only money above this is taxable. Note that this limit is per person, giver and receiver, so if either your mom or you are married, both parents could gift each to both of you each 15000 tax free, resulting in 60000 tax free.
There are no tax consequences of using any amount you happen to have to pay off part of your mortgage.
Make sure you do it right, as some mortgage companies have funny rules about larger payments - they could consider it a 'pre-payment of your next N monthly payments' and as such just 'safekeep it interest free' for you, and pay your monthly rate every month from it. This is obviously bad for you, and not what you want; you want it applied to the principal immediately, so make sure this is what happens.
Overall, no paperwork, and no tax consequences for you. No worries.