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It is said that, when one becomes a Sannyasin, he renounces all possessions. He lives alone on alms and spends his time in meditation. When he attains the sublime state of deep meditation he rejoices in the Self. He is quite indifferent to sensual pleasures. He is free from likes and dislikes, desires, egoism, lust, anger, greed and pride. He has equal vision and balanced mind. He disseminates Brahma Jnana or Knowledge of the Self. And is the same in honour and dishonour, praise and censure, success and failure. At this stage he becomes Ativarnashrami, i.e., above Varna and Ashrama. He is quite a free man, not bound by any social customs and conventions. Such a Sannyasin is referred to as an ideal. The Bhagavata Purana describes the ideal nature of a Sannyasi as follows:
सुशीलो मितभुग्दक्षः श्रद्दधानो जितेन्द्रियः । यावदर्थं व्यवहरेत्स्त्रीषु स्त्रीनिर्जितेषु च ॥ ६॥suśīlo mitabhugdakṣaḥ śraddadhāno jitendriyaḥ । yāvadarthaṁ vyavaharetstrīṣu strīnirjiteṣu ca ॥ 6॥
Meaning: He should be of a good character, moderate in eating, alert and prompt (in work), of reverential faith in shastras and self-controlled. It is only when absolutely necessary and to that much extent only that he should deal with women (eg. for getting alms) or with those who are influenced by women.
सन्न्यासधर्मः ॥ Code of Conduct
If a person is capable and fit (physically and mentally), he should take to the life of a wandering hermit (Sannyasi). Owning nothing else except his body, he should observe the rule of staying one night in a village, and thus wander over the earth, being totally desireless.
कल्पस्त्वेवं परिव्रज्य देहमात्रावशेषितः । ग्रामैकरात्रविधिना निरपेक्षश्चरेन्महीम् ॥ १॥kalpastvevaṁ parivrajya dehamātrāvaśeṣitaḥ । grāmaikarātravidhinā nirapekṣaścarenmahīm ॥ 1॥
A person in the renounced order of life may try to avoid even a dress to cover himself. It he wears anything at all, it should only be a loincloth, and when there is no necessity, a sannyasi should not even accept a danda. A sannyasi should avoid carrying anything but a danda and kamandalu.
बिभृयाद्यद्यसौ वासः कौपीनाच्छादनं परम् । त्यक्तं न दण्डलिङ्गादेरन्यत्किञ्चिदनापदि ॥ २॥bibhr̥yādyadyasau vāsaḥ kaupīnācchādanaṁ param । tyaktaṁ na daṇḍaliṅgāderanyatkiñcidanāpadi ॥ 2॥
According to the Bhagavata, a sannyasi should wander all alone as a mendicant subsisting on alms, delighted in his own Self and seeking no shelter. He should be friendly to all beings, serene and devoted exclusively to Narayana.
एक एव चरेद्भिक्षुरात्मारामोऽनपाश्रयः । सर्वभूतसुहृच्छान्तो नारायणपरायणः ॥ ३॥eka eva caredbhikṣurātmārāmo'napāśrayaḥ । sarvabhūtasuhr̥cchānto nārāyaṇaparāyaṇaḥ ॥ 3॥
He should visualize this universe in the immutable atman who is beyond (and distinct from) cause and effect and should perceive the Self as the Supreme Brahman present everywhere in the Universe , (a product) of causes and consequences. 
पश्येदात्मन्यदो विश्वं परे सदसतोऽव्यये । आत्मानं च परं ब्रह्म सर्वत्र सदसन्मये ॥ ४॥paśyedātmanyado viśvaṁ pare sadasato'vyaye । ātmānaṁ ca paraṁ brahma sarvatra sadasanmaye ॥ 4॥
During the mediate state between sleep and wakefulness, one should concentrate on the atman within, and should try to perceive the true nature of the Self. He should look upon bondage and emancipation as merely illusory and not real.
सुप्तिप्रबोधयोः सन्धावात्मनो गतिमात्मदृक् । पश्यन् बन्धं च मोक्षं च मायामात्रं न वस्तुतः ॥ ५॥suptiprabodhayoḥ sandhāvātmano gatimātmadr̥k । paśyan bandhaṁ ca mokṣaṁ ca māyāmātraṁ na vastutaḥ ॥ 5॥
He should welcome neither death, which is inevitable, nor life that is transitory. But he should simply wait for the time which brings about the birth and death of beings (and that of one's body as well).
नाभिनन्देद्ध्रुवं मृत्युमध्रुवं वास्य जीवितम् । कालं परं प्रतीक्षेत भूतानां प्रभवाप्ययम् ॥ ६॥nābhinandeddhruvaṁ mr̥tyumadhruvaṁ vāsya jīvitam । kālaṁ paraṁ pratīkṣeta bhūtānāṁ prabhavāpyayam ॥ 6॥
He should not be attached to Shastras dealing with topics other than atman. Nor should he try to maintain himself by following any profession (like astrology, medicine practised by him as a grhastha). He should avoid all form of disputation. He should not persistently adhere to any party.
नासच्छास्त्रेषु सज्जेत नोपजीवेत जीविकाम् । वादवादांस्त्यजेत्तर्कान् पक्षं कं च न संश्रयेत् ॥ ७॥nāsacchāstreṣu sajjeta nopajīveta jīvikām । vādavādāṁstyajettarkān pakṣaṁ kaṁ ca na saṁśrayet ॥ 7॥
He should not attract students. Nor should he study numerous books (lest they should cause confusion or distraction). He should not undertake the exposition of some sacred text (other than those on Vedanta). Nor should he take up the establishment of any institution or monastery.
न शिष्याननुबध्नीत ग्रन्थान् नैवाभ्यसेद्बहून् । न व्याख्यामुपयुञ्जीत नारम्भानारभेत्क्वचित् ॥ ८॥na śiṣyānanubadhnīta granthān naivābhyasedbahūn । na vyākhyāmupayuñjīta nārambhānārabhetkvacit ॥ 8॥
The duties etc. prescribed for the sannyasins are not meant for securing religious merit in the case of the paramahamsas who are of serene and equable minds. (The rules are to be observed till the sanyasi realizes the highest wisdom). Thereafter, he may continue to practise the rules (for setting up an ideal life before the public) or discard them.
न यतेराश्रमः प्रायो धर्महेतुर्महात्मनः । शान्तस्य समचित्तस्य बिभृयादुत वा त्यजेत् ॥ ९॥na yaterāśramaḥ prāyo dharmaheturmahātmanaḥ । śāntasya samacittasya bibhr̥yāduta vā tyajet ॥ 9॥
The Bhagavata Purana further says,
अव्यक्तलिङ्गो व्यक्तार्थो मनीष्युन्मत्तबालवत् । कविर्मूकवदात्मानं स दृष्ट्या दर्शयेन्नृणाम् ॥ १०॥avyaktaliṅgo vyaktārtho manīṣyunmattabālavat । kavirmūkavadātmānaṁ sa dr̥ṣṭyā darśayennr̥ṇām ॥ 10॥
Meaning: Although a wise person may not expose himself to the vision of human society, by his behaviour his purpose is disclosed. To human society, he should present himself like a restless child, and although he is the greatest thoughtful orator, he should present himself like a dumb man.
In this regard, the Bhagavata Purana enumerates a conversation between Raja Prahlada and the sage Dattatreya.
यत्रास्तमितशायी स्यान्निरग्निरनिकेतनः। यथोपलब्धजीवी स्यान्मुनिर्दान्तो जितेन्द्रियः।।12.60.8 (61.8)
निराशीर्निर्नमस्कारो निर्भोगो निर्विकारवान्। विप्रः क्षेमाश्रमं प्राप्तो गच्छत्यक्षरसात्मताम्।। 9
स्त्रीषु व्यवहारः ॥ Behaviour with women
The Bhagavata Purana explains that so long as by self realization one has not firmly determined that his body, senses or the universe etc. are illusory and the jiva has not attained perfect mastery over himself by identifying himself with the Supreme being, the notion of duality (between a man and a woman) will continue to persist (provoking thereby the desire to enjoy) through false attribution of gunas (Bha.Pur.7.12.10).
Therefore, it says that a person other than a householder, who has taken the great vow of celibacy, should avoid all talk with young women. For, the senses are (by nature) so powerful and violent that they carry away the mind of even a Yati (recluse) who is expected to be perfectly self-controlled (Bha.Pur.7.12.7)
कल्पयित्वाऽऽत्मना यावदाभासमिदमीश्वरः । द्वैतं तावन्न विरमेत्ततो ह्यस्य विपर्ययः ॥ १०॥
वर्जयेत्प्रमदागाथामगृहस्थो बृहद्व्रतः । इन्द्रियाणि प्रमाथीनि हरन्त्यपि यतेर्मनः ॥ ७॥
kalpayitvā''tmanā yāvadābhāsamidamīśvaraḥ । dvaitaṁ tāvanna viramettato hyasya viparyayaḥ ॥ 10॥
varjayetpramadāgāthāmagr̥hastho br̥hadvrataḥ । indriyāṇi pramāthīni harantyapi yatermanaḥ ॥ 7॥
Being in control of the mind is emphasized in the life of a Sannyasi. In this regard, the Bhagavata Purana (Skandha 7, Adhyaya 15) says that he who has resolved to subjugate his mind should dissociate himself from all attachments and belongings; he should become a recluse and live alone in secluded place, eating moderately what he gets as alms.
यश्चित्तविजये यत्तः स्यान्निःसङ्गोऽपरिग्रहः | एको विविक्तशरणो भिक्षुर्भैक्ष्यमिताशनः ||३०||yaścittavijayē yattaḥ syānniḥsaṅgō'parigrahaḥ | ēkō viviktaśaraṇō bhikṣurbhaikṣyamitāśanaḥ ||30||
Rajadharmanushasana Parva, Shanti Parva
प्राहुश्चतुर्थं ब्रह्मणेरितम्।।12.60.2 (61.2)
The fourth ashrama (Sannyasashrama) is upheld only by brahmanas.
चरितब्रह्मचर्यस्य ब्राह्मणस्य विशांपते। भैक्षचर्यास्वधीकारः प्रशस्तो देहमोक्षणे।।12.60.7(61.7)
The one who has upheld brahmacharya, if such a brahmachari wishes for moksha, then he is bestowed with the authority/eligibility to directly take to Sannyasa following the brahmacharyashrama.
यत्रास्तमितशायी स्यान्निरग्निरनिकेतनः। यथोपलब्धजीवी स्यान्मुनिर्दान्तो जितेन्द्रियः।।12.60.8(61.8)
A Sannyasi should live like a sage by keeping his sense organs and mind under control, not desire for an object, not construct a math or kutir for oneself, always keep wandering and stay wherever one is during sunset and lead life with whatever is obtained by fate.
निराशीर्निर्नमस्कारो निर्भोगो निर्विकारवान्। विप्रः क्षेमाश्रमं प्राप्तो गच्छत्यक्षरसात्मताम्।।12.60.9(61.9)
One should give up wants and greed and treat everyone equally. Should stay away from materialistic enjoyments and never let deflections arise in one's heart. Because of these dharmas Vanaprashthashrama is also known as Kshemashrama (the stage that helps attain prosperity). A brahmana in this ashrama attains oneness with the indestructible brahman.
Uma Shankara Samvada, Anushasana Parva, Mahabharata.
यतिधर्मास्तथा देवि गृहांस्त्यक्त्वा यतस्ततः। आकिञ्चन्यमनारम्भः सर्वतः शौचमार्जवम्।।13.208.51
सर्वत्र भैक्षचर्या च सर्वत्रैव विवासनम्। सदा ध्यानपरत्वं च देहशुद्धिः क्षमा दया। तत्वानुगतबुद्धित्वं तस्य धर्मविधिर्भवेत्।।13.208.52
Yati dharma states that a sannyasi should abandon his house and wander here and there. He should not collect anything for himself. He should stay away from starting or building karmans. He should establish within himself purity and simplicity from all perspectives. He should lead life by bhiksha. He should be detached from all places. He should always be engaged in meditation, be free from doshas, have kshama and daya towards all and always engage his mind in the contemplation of the essence - these are the duties of a Sannyasi.
वृक्षमूलचरो नित्यं शून्यागारिनिवेशनमम्।।13.211.56
नदीपुलिनशायी च नदीतीरमनुव्रजन्। विमुक्तः सर्वसङ्गेभ्यः स्नेहबन्धेन वै द्विजः। 13.211.57
आत्मन्येवात्मना भावं समायोज्येह तेन वै।13.211.58
A sannyasi dvija being free from all attachments and bonds of love should always live under a tree or empty house or bank of a river and contemplate on the Paramatma in his mind.
- Swami Sivananda (1999), All About Hinduism, Uttar Pradesh: The Divine Life Society.
- Bhagavata Purana, Skandha 7, Adhyaya 12.
- Ganesh Vasudeo Tagare, The Bhagavata Purana (Part III), Ancient Indian Tradition & Mythology (Volume 9), Edited by J.L.Shastri, New Delhi: Motilal Banarsidass, P.no.968-969.
- Ganesh Vasudeo Tagare, The Bhagavata Purana (Part III), Ancient Indian Tradition & Mythology (Volume 9), Edited by J.L.Shastri, New Delhi: Motilal Banarsidass, P.no.973-975.
- Bhagavata Purana, Skandha 7, Adhyaya 13.
- A.C.Bhaktivedanta Swami Prabhupada, Srimad Bhagavatam (Seventh Canto), Part 3-Chapters 10-15, 1976: Bhaktivedanta Book Trust.
- Mahabharata, Shanti Parva, Adhyaya 60
- Ganesh Vasudeo Tagare, The Bhagavata Purana (Part III), Ancient Indian Tradition & Mythology (Volume 9), Edited by J.L.Shastri, New Delhi: Motilal Banarsidass, P.no.985-996.
- Bhagavata Purana, Skandha 7, Adhyaya 15.
- Pandit Ramnarayanadatta Shastri Pandey, Mahabharata (Khanda 5-Shantiparva), Gorakhpur: Gita Press.
- Mahabharata, Anushasana Parva, Adhyaya 208
- Shastri, Ramnarayanadatta Pandey, Mahabharata Volume 6 (With Hindi Translation), Gorakhpur:Gita Press.
- Mahabharata, Anushasana Parva, Adhyaya 211