Verse 3.13.8

तस्यैषा दृष्टिर्यत्रितदस्मिञ्छरीरे संस्पर्शेनोष्णिमानं विजानाति तस्यैषा श्रुतिर्यत्रैतत्कर्णावपिगृह्य निनदमिव नदथुरिवाग्नेरिव ज्वलत उपशृणोति तदेतद्दृष्टं च श्रुतं चेत्युपासीत चक्षुष्यः श्रुतो भवति य एवं वेद य एवं वेद ॥ ३.१३.८ ॥
॥ इति त्रयोदशः खण्डः ॥

tasyaiṣā dṛṣṭiryatritadasmiñcharīre saṃsparśenoṣṇimānaṃ vijānāti tasyaiṣā śrutiryatraitatkarṇāvapigṛhya ninadamiva nadathurivāgneriva jvalata upaśṛṇoti tadetaddṛṣṭaṃ ca śrutaṃ cetyupāsīta cakṣuṣyaḥ śruto bhavati ya evaṃ veda ya evaṃ veda || 3.13.8 ||
|| iti trayodaśaḥ khaṇḍaḥ ||

8. Here is proof of it: When you touch the body you can feel heat in it. There is also an audible proof of it: When you cover your ears you can hear a sound like a moving chariot, or like the bellowing of a bullock, or like a burning fire. A person should meditate on that light in the body as something that is seen and heard. He who knows this becomes a distinguished person—people want to see him and he is widely known.

Word-for-word explanation:

Tasya, its [i.e., of the Self in the bodies]; eṣā dṛṣṭiḥ, this visible [proof]; yatra, when; etat asmin śarīre, in this body; saṃsparśena, by touch; uṣṇimānam, warmth; vijānāti, one can feel; tasya eṣā śrutiḥ, this audible [proof] of it; yatra etat karṇau apigṛhya, when one covers the ears; ninadam iva, like the sound of a moving chariot; nadathuḥ iva, like the bellowing of a bullock; agneḥ iva jvalataḥ, like the sound of a burning fire; upaśṛṇoti, one can hear; tat etat, that [light]; iti upāsīta, one should meditate on; dṛṣṭam ca śrutam ca, as seen and as heard; yaḥ evam veda, he who knows this; cakṣuṣyaḥ śrutaḥ bhavati, becomes worth seeing and famous. Iti trayodaśaḥ khaṇḍaḥ, here ends the thirteenth section.

Commentary:

What proof is there that there is any light in the heart? One proof is the warmth of the body. This warmth comes from the light within. But there is yet another proof: If you cover your ears you will hear all manner of sounds. The sounds and the feeling of warmth both prove that Brahman is within.