New York Codes, Rules and Regulations
Title 20 - DEPARTMENT OF TAXATION AND FINANCE
Chapter II - Income Taxes and Estate Taxes
Subchapter A - New York State Personal Income Tax Under Article 22 Of The Tax Law
Article 3 - Nonresidents
Part 137 - Nonresident Partners
Section 137.1 - Partnership income and deductions of nonresident partner derived from New York State sources

Tax Law, § 637(a)

The New York source income of a nonresident partner includes the partner's distributive share of all items of partnership income, gain, loss and deduction entering into such partner's Federal adjusted gross income to the extent such items are derived from or connected with New York State sources, i.e.,attributable to the ownership by the partnership of any interest in real or tangible personal property in New York State or to a business, trade, profession or occupation carried on in New York State by the partnership as determined under sections 132.3, 132.4(a), 132.6, 132.9, 132.12 -132.16, 132.21 and 132.22 of this article and 137.2 of this Part.