This seems applicable as well:
https://www.law.cornell.edu/cfr/text/26/1.408A-6
Q-1. How are distributions from Roth IRAs taxed?
(d) Contributions that are returned to the Roth IRA owner in accordance with section 408(d)(4) (corrective distributions) are not includible in gross income, but any net income required to be distributed under section 408(d)(4) together with the contributions is includible in gross income for the taxable year in which the contributions were made.
