Mbh 13.104.2h

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. At daytime both calls of nature should be answered with face turned towards the north. At night, those calls should be answered facing the south. By so doing one does not shorten one's life. One that wishes to live long should never disregard or insult any of these three, however weak or emaciated they may appear to be, viz., the Brahmana, the Kshatriya, and the snake. All three are endued with virulent poison. The snake, if angry, burns the victim with only a glance of its eyes. The Kshatriya also, if angry, burns the objects of his wrath, as soon as he sees him, with his energy. The Brahmana, stronger than any of these two, destroys not only the objects of his wrath but his whole race as well, not by vision alone but by thought also.[466] The man of wisdom should, therefore, tend these three with care. One should never engage in any disputation with one's preceptor. O Yudhishthira, if the preceptor becomes angry, he should always be pacified by due honours being paid to him. Even if the preceptor happens to be entirely wrong, one should still follow and honour him. Without doubt, calumnious sayings against the preceptor always consume the lives of those that utter them. One should always answer a call of nature at a spot far removed from one's habitation. One should wash one's feet at a distance from one's habitation. One should always throw the remnants of one's dishes and plates at a spot far removed from one's habitation. Verily, he who desires his own good should do all these.