Mundaka 2.12

परीक्ष्य लोकान् कर्मचितान् ब्राह्मणो निर्वेदमायात् नास्त्यकृतः कृतेन। तद्विज्ञानार्थं स गुरुमेवाभिगच्छेत् समित्पाणिः श्रोत्रियं ब्रह्मनिष्ठम् ॥१२॥

parīkṣya lokān karmacitān brāhmaṇo nirvedamāyāt nāstyakṛtaḥ kṛtena। tadvijñānārthaṃ sa gurumevābhigacchet samitpāṇiḥ śrotriyaṃ brahmaniṣṭham ॥12॥

[परीक्ष्य (parīkṣya) - having examined; लोकान् (lokān) - worlds; कर्मचितान् (karmacitaān) - built by actions; ब्राह्मणः (brāhmaṇaḥ) - a Brahmin; निर्वेदम् (nirvedam) - dispassion; आयाति (āyāti) - comes; न (na) - not; अस्ति (asti) - is; अकृतः (akṛtaḥ) - uncreated; कृतेन (kṛtena) - by actions; तत् (tat) - that; विज्ञानार्थम् (vijñānārtham) - for the sake of knowledge; सः (saḥ) - he; गुरुम् (gurum) - to the guru; एव (eva) - indeed; अभिगच्छेत् (abhigacchet) - should approach; समित्पाणिः (samitpāṇiḥ) - with sacrificial fuel in hand; श्रोत्रियम् (śrotriyam) - a learned one; ब्रह्मनिष्ठम् (brahmaniṣṭham) - established in Brahman;]

After examining the worlds created by actions, a Brahmin becomes dispassionate, realizing that the eternal cannot be achieved through actions. To gain this knowledge, he should indeed approach the guru, who is both learned and established in Brahman, carrying sacrificial fuel.