SB 3.21.45-47

praviśya tat tīrtha-varam
 ādi-rājaḥ sahātmajaḥ
dadarśa munim āsīnaṁ
 tasmin huta-hutāśanam
vidyotamānaṁ vapuṣā
 tapasy ugra-yujā ciram
nātikṣāmaṁ bhagavataḥ
 snigdhāpāṅgāvalokanāt
tad-vyāhṛtāmṛta-kalā-
 pīyūṣa-śravaṇena ca
prāṁśuṁ padma-palāśākṣaṁ
 jaṭilaṁ cīra-vāsasam
upasaṁśritya malinaṁ
 yathārhaṇam asaṁskṛtam
Word for word: 
praviśya — entering; tat — that; tīrtha-varam — best of sacred places; ādi-rājaḥ — the first monarch (Svāyambhuva Manu); saha-ātmajaḥ — along with his daughter; dadarśa — saw; munim — the sage; āsīnam — sitting; tasmin — in the hermitage; huta — being offered oblations; huta-aśanam — the sacred fire; vidyotamānam — shining brilliantly; vapuṣā — by his body; tapasi — in penance; ugra — terribly; yujā — engaged in yoga; ciram — for a long time; na — not; atikṣāmam — very emaciated; bhagavataḥ — of the Lord; snigdha — affectionate; apāṅga — sidelong; avalokanāt — from the glance; tat — of Him; vyāhṛta — from the words; amṛta-kalā — moonlike; pīyūṣa — the nectar; śravaṇena — by hearing; ca — and; prāṁśum — tall; padma — lotus flower; palāśa — petal; akṣam — eyes; jaṭilam — matted locks; cīra-vāsasam — having rags for clothes; upasaṁśritya — having approached; malinam — soiled; yathā — like; arhaṇam — gem; asaṁskṛtam — unpolished.
Translation: 
Entering that most sacred spot with his daughter and going near the sage, the first monarch, Svāyambhuva Manu, saw the sage sitting in his hermitage, having just propitiated the sacred fire by pouring oblations into it. His body shone most brilliantly; though he had engaged in austere penance for a long time, he was not emaciated, for the Lord had cast His affectionate sidelong glance upon him and he had also heard the nectar flowing from the moonlike words of the Lord. The sage was tall, his eyes were large, like the petals of a lotus, and he had matted locks on his head. He was clad in rags. Svāyambhuva Manu approached and saw him to be somewhat soiled, like an unpolished gem.
Purport: 

Here are some descriptions of a brahmacārī-yogī. In the morning, the first duty of a brahmacārī seeking spiritual elevation is huta-hutāśana, to offer sacrificial oblations to the Supreme Lord. Those engaged in brahmacarya cannot sleep until seven or nine o’clock in the morning. They must rise early in the morning, at least one and a half hours before the sun rises, and offer oblations, or in this age, they must chant the holy name of the Lord, Hare Kṛṣṇa. As referred to by Lord Caitanya, kalau nāsty eva nāsty eva nāsty eva gatir anyathā: there is no other alternative, no other alternative, no other alternative, in this age, to chanting the holy name of the Lord. The brahmacārī must rise early in the morning and, after placing himself, should chant the holy name of the Lord. From the very features of the sage, it appeared that he had undergone great austerities; that is the sign of one observing brahmacarya, the vow of celibacy. If one lives otherwise, it will be manifest in the lust visible in his face and body. The word vidyotamānam indicates that the brahmacārī feature showed in his body. That is the certificate that one has undergone great austerity in yoga. A drunkard or smoker or sex-monger can never be eligible to practice yoga. Generally yogīs look very skinny because of their not being comfortably situated, but Kardama Muni was not emaciated, for he had seen the Supreme Personality of Godhead face to face. Here the word snigdhāpāṅgāvalokanāt means that he was fortunate enough to see the Supreme Lord face to face. He looked healthy because he had directly received the nectarean sound vibrations from the lotus lips of the Personality of Godhead. Similarly, one who hears the transcendental sound vibration of the holy name of the Lord, Hare Kṛṣṇa, also improves in health. We have actually seen that many brahmacārīs and gṛhasthas connected with the International Society for Krishna Consciousness have improved in health, and a luster has come to their faces. It is essential that a brahmacārī engaged in spiritual advancement look very healthy and lustrous. The comparison of the sage to an unpolished gem is very appropriate. Even if a gem just taken from a mine looks unpolished, the luster of the gem cannot be stopped. Similarly, although Kardama was not properly dressed and his body was not properly cleansed, his overall appearance was gemlike.