N.Y. Correct. Law § 354

§ 354. Copy of sentence and affidavit to be presented. The petition\nmust be accompanied with a copy of the sentence of conviction of the\nprisoner, duly certified by the clerk of the court by which he was\nsentenced, under the seal thereof; together with an affidavit of the\napplicant, stating that the person so convicted is actually imprisoned\nthereunder.\n