KAṬHA UPANISHAD · 2.3.9

न संदृशे तिष्ठति रूपमस्य
न चक्षुषा पश्यति कश्चनैनम् ।
हृदा मनीषा मनसाऽभिकॢप्तो
य एतद्विदुरमृतास्ते भवन्ति ॥ ९॥

na saṃdṛśe tiṣṭhati rūpamasya
na cakṣuṣā paśyati kaścanainam ।
hṛdā manīṣā manasā’bhikḷpto
ya etadviduramṛtāste bhavanti ॥ 9॥

He hath not set His body within the ken of seeing, neither doth any man with the eye behold Him, but to the heart and mind and the supermind He is manifest. Who know Him are the immortals.