I have heard many times that if there is any funeral then probably we burn the deceased person. But in case of death of a Sannyasi we do not burn his body rather bury in the ground.
This is even true for baby. If there is death of baby then we either bury it of leave it in any river.
Could somebody tell me exactly why we do this.
Who is a Sannyasi and how do the scriptures describe an ideal Sannyasi can be read here
Why do we cremate?
Hindus traditionally cremate their dead because a fiery dissolution of the body brings swifter, more complete release of the soul than burial, which preserves the soul's psychic connection to its just-ended earthly life. After death, the departed soul hovers close to the earth plane in its astral body, emotionally attached to the physical body and its old surroundings, still able to see this material world. The funeral rites and burning of the body signify spiritual release, notifying the soul that, in fact, death has come. Some of the funeral chants address the deceased, urging the soul to relinquish attachments and continue its spiritual journey. The Gods and devas are invoked to assist the soul in its transition. The fire severs ties to earthly life and gives momentum to the soul, granting at least momentary access to refined, heavenly realms. All attention is on a singular goal, as expressed in this prayer from the Rig Veda:
"Release him again, O Agni, to the fathers. The one offered to you now proceeds to his destiny. Putting on new life, let him approach the surviving, let him reunite with a [new] body, All-Knowing One!" (10. 16. 5).
So a person is cremated for his soul to achieve after death what a sannyasi has already achieved before death.
The sannyasin has no sacrament involving the sacred fire: he has the fire of knowledge (jnanagni)in him. His body is not cremated - that is there is no Agni-samskara for it- but interred as a matter of respect. Strictly speaking, it must be cut into four parts and consigned to the four quarters of a forest. There it will be food for birds and beasts. In an inhabited place the severed parts of the body would cause inconvenience to people. That is why they were thrown into the forest. There it would be food for its denizens; if buried it would be manure for the plants. Now over the site of the interment of a sannyasin's body a Brindavana is grown [or built] : this again is done out of respect. At such sites all that is to be done is to plant a bilva or asvattha tree.
When the Yogi separates himself from the physical body at the time of death, Brahmarandhra bursts open and Prana comes out through this opening (Kapala Moksha). “A hundred and one are the nerves of the heart. Of them one (Sushumna) has gone out piercing the head; going up through it, one attains immortality” (Kathopanishad).
To attain this or symbolically yogis and sanyasins after death are placed in yoga posture. Sometimes kapala moksha is made by throwing a coconut on the head. Then the mortal body is buried.
Brahmarandhra: When the Yogi separates himself from the physical body at the time of death, this Brahmarandhra bursts open and Prana comes out through this opening (Kapala Moksha). “A hundred and one are the nerves of the heart. Of them one (Sushumna) has gone out piercing the head; going up through it, one attains immortality” (Kathopanishad).
Why bury children?
Cremation is the norm in Hinduism to dispose of the dead body. However, this norm does not apply to children. The bodies of young children who die within a year from the date of their birth are usually buried rather than cremated. In some instances they are consigned to rivers. In other words their bodies are offered to water or the earth, rather than fire. It is because the subtle bodies of children remain underdeveloped and hence unfit for fire sacrifice.
The final rites of a burial, in case of untimely death of a child, is rooted in Rig Veda's section 10.18, where the hymns mourn the death of the child, praying to deity Mrityu to "neither harm our girls nor our boys", and pleads the earth to cover, protect the deceased child as a soft wool.
Betake thee to the Iap of Earth the Mother, of Earth far-spreading, very kind and gracious. Young Dame, wool-soft unto the guerdongiver, may she preserve thee from Destruction's bosom.
For the Sannyasis, there is an explanation given in the so-called Sannyasa Upanishads, which are all minor Upanishads.
I am quoting from the Paingala Upanishad that is linked with the Shukla Yajurveda:
He gives up his body whether in a sacred place, or in a chandala s (outcaste s) house (without any distinction whatever), and attains salvation. Such a body (when seen by a person) should be offered as a sacrifice to dik (the quarters) or should be buried (underground). It is only to Purusha (the wise) that sannyasa (renunciation) is ordained and not to others. In case of the death of an ascetic who is of the form (or has attained the nature) of Brahman, there is no pollution (to be observed) ; neither the ceremonies of fire (as burning the body, homa, eta) ; nor the pinda (balls of rice), nor ceremonies of water, nor the periodical ceremonies (monthly and yearly). Just as a food once cooked is not again cooked, so a body once burnt (by the fire of wisdom) should not be burnt (or exposed to fire) again. To one whose body was burnt by the fire of wisdom there is neither sraddha (required to be performed), nor (funeral) ceremony.
From the Upanishad's 4th Adyayaya.
So, food once cooked is not to be cooked again--is the logic being provided.
Another relevant verse from another Sannyasa Upanishad:
Triple staff, sacrificial string, loincloth, sling, and water strainer: these he should carry all his life. These are the five articles of a renouncer. They are declared to be the five parts of Brahman.5 Let him not abandon them until death. Even at death he should be buried with them.6
Satyayaniya Upanishad
As regards, the children, then we find the scriptural injunctions, but i don't think we can find the reasons as well:
Immediate is [the purification, on the death of a child] who has not teethed ; [and impurity extends over] one night, before the ceremony of tonsure (Chuddkaranam) [is performed within two years] ; and three nights,, before the investiture with the sacred thread (Upanayanam] ; and ten nights, afterwards. (13)
Usana Smriti verses
When a child dies before it is 3 years old or before teething, no offerings of food or water are prescribed, and it should not be cremated.
Baudhayana Dharma Sutras 1.11.7
So, IMO impurities do not result from a child's death depending on whether it had teethed or not and also on few other factors.
Mahanirbana Tantra categorically says that
The corpse of an ascetic should on no account be cremated. It should be worshipped with scents and flowers, and then either buried or sunk into water. - Mahanirvana Tantra 8.284
Mahanirbana Tantra is one the 64 principal Shakta Tantras (List from Sarvollasa Tantra of Sarvanandanatha). So this is the Agamic practice.
Reference -
