The Imam narrates from his teacher, Muhammad bin Yahya, with his chain of transmission. In the narration of Muqar ‘Affan, these words are not present: "Then the Prophet (peace be upon him) put his hand inside his garment."
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الأفعال المباحة فى الصلاة / 906