Chandogya Upanishad
Prapathaka VII, Khanda 15
'Spirit (prâna) is better than hope. As the spokes of a wheel hold to the nave , so does all this (beginning with names and ending in hope) hold to spirit. That spirit moves by the spirit, it gives spirit to the spirit. Father means spirit, mother is spirit, brother is spirit, sister is spirit, tutor is spirit, Brâhmana is spirit.
'For if one says anything unbecoming to a father, mother, brother, sister, tutor or Brâhmana, then people say, Shame on thee! thou hast offended thy father, mother, brother, sister, tutor, or a Brâhmana.
'But, if after the spirit has departed from them, one shoves them together with a poker, and burns them to pieces, no one would say, Thou offendest thy father, mother, brother, sister, tutor or a Brâhmana.