Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 22
ये देहभाजस्त्रिगुणप्रधानागुणान् विपश्यन्त्युत वा तमश्च ।यन्मायया मोहितचेतसस्त्वांविदु: स्वसंस्थं न बहि:प्रकाशा: ॥ २२ ॥
ye deha-bhājas tri-guṇa-pradhānāguṇān vipaśyanty uta vā tamaś cayan-māyayā mohita-cetasas tvāṁviduḥ sva-saṁsthaṁ na bahiḥ-prakāśāḥ
My Lord, You are fully situated in everyone’s heart, but the living entities, covered by the material body, cannot see You, for they are influenced by the external energy, conducted by the three modes of material nature. Their intelligence being covered by sattva-guṇa, rajo-guṇa and tamo-guṇa, they can see only the actions and reactions of these three modes of material nature. Because of the actions and reactions of the mode of ignorance, whether the living entities are awake or sleeping, they can see only the workings of material nature; they cannot see Your Lordship.
Unless one is situated in the transcendental loving service of the Lord, one is unable to understand the Supreme Personality of Godhead. The Lord is situated in everyone’s heart. However, because the conditioned souls are influenced by material nature, they can see only the actions and reactions of material nature, but not the Supreme Personality of Godhead. One therefore must purify himself internally and externally: To keep ourselves externally clean we should bathe three times daily, and for internal cleanliness we must cleanse the heart by chanting the Hare Kṛṣṇa mantra. The members of the Kṛṣṇa consciousness movement must always follow this principle (bāhyābhyantaraḥ śuciḥ). Then it will one day be possible to see the Supreme Personality of Godhead face to face.