I assume you got a 1099R with the withholding in box 4? That will show up on 1040 line 25b.
You didn't actually pay the tax. You had taxes withheld like from your paycheck. You still have to enter the whole gross amount (before taxes were withheld) with your other income to figure out the total tax (and it may put you into a higher tax bracket and can reduce any credits) and then the withholding is subtracted from the total tax to figure your refund or tax due. The Gross amount shows up on 1040 line 4a or 5a and the taxable amount on 4b/5b. The withholding will show up on 1040 line 25b.
