Mahabharata Anushasna Parva Chapter 104:5

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 104:5 One should never answer a call of nature in a standing posture. One should never answer a call of nature on ashes or in a cow-pen. One should wash one's feet before sitting to one's meals. One should never sit or lie down for sleep with wet feet. One who sits to one's meals after having washed one's feet, lives for a hundred years. One should never touch these three things of great energy, while one is in an impure state, viz., fire, a cow, and a Brahmana. By observing this rule, one acquires longevity. One should not, while one is in an impure state, cast one's eyes on these three things of great energy, viz., the sun, the moon, and the stars. The life-breaths of a young man go upwards when an old and venerable person comes to his abode. He gets them back by standing up and properly saluting the guest. Old men should always be saluted. One should, upon seeing them, offer seats with one's own hand. After the old man has taken his seat, one should seat oneself and remain with hands joined in reverence. When an old man goes along the road, one should always follow him instead of walking ahead. One should never sit on a torn or broken seat. One should, without using it any longer, cast away a broken vessel of white brass. One should never eat without a piece of upper garment wrapping one's body. One should never bathe in a state of nudity. One should never sleep in a state of nudity. One should never even touch the remnants of other people's dishes and plates. One should never, while one is in an impure state, touch another's head, for it is said in the scriptures that the life-breaths are all concentrated in the head. One should never strike another on the head or seize another by the hair. One should not join one's hands together for scratching one's head. One should not, while bathing, repeatedly dip one's head in water. By so doing one shortens one's life. One who has bathed by dipping the head in water should not, afterwards, apply oil to any part of one's body. One should never take a meal without eating some sesame. One should never teach (the Vedas or any scriptures) at a time when one is impure. Nor should one study while one is impure. When a storm rises or a bad odour permeates in the atmosphere, one should never think of the Vedas. Persons conversant with ancient history recite a Gatha sung by Yama in days of old. He that runs while impure or studies the Vedas under similar circumstances, indeed, that regenerate Brahman who studies the Vedas at forbidden times, loses his Vedas and shortens his life. Hence, one should never study the Vedas with concentrated attention at forbidden times. They who answer a call of nature, with face towards the sun, or towards a blazing fire, or towards a cow, or towards a regenerate person, or on the road, become shortlived.