Bhagavad Gita 13.2
Lord Shri Krishna replied: O Arjuna! The body of a person is the playground of the Self; and That which knows the activities of Matter, sages call the Self.
श्री भगवानुवाचइदं शरीरं कौन्तेय क्षेत्रमित्यभिधीयते।एतद्यो वेत्ति तं प्राहुः क्षेत्रज्ञ इति तद्विदः॥śrī bhagavānuvācaidaṃ śarīraṃ kaunteya kṣetramityabhidhīyate|etadyo vetti taṃ prāhuḥ kṣetrajña iti tadvidaḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).