26 USC 501 (2012): Exemption from tax on corporations, certain trusts, etc. (Note: "(c)(3)" is a provision of this section)
26 CFR 1.501(C)(3)-1 (2019): Organizations organized and operated for religious, charitable, scientific, testing for public safety, literary, or educational purposes, or for the prevention of cruelty to children or animals.
Written by Bruce Hopkins, the foremost expert on nonprofit law, this is your complete analysis of the procedures and practices of the IRS in its audits of tax-exempt organizations. Practical in presentation, this book offers advice on undergoing audits, details today's exempt organizations' issues, and authoritatively examines detailed documentation and citations, as well as numerous case studies, tips, forms, and checklists.
IRS, Publications 557: Tax-Exempt Status for Your Organization (Rev. January 2019).