Are there any instances in our itihas shastras where brahmin did work out of what is precribed in scriptures(i.e teaching)? E.G Dronacharya and kripacharya fought for kauravas!
do a brahmin incur sin if he does work out of what is prescribed in scriptures?
There are only certain occupations that are prescribed for the Brahmins. See the following verses:
Manu Smriti 10.75. Teaching, studying, sacrificing for himself, sacrificing for others, making gifts and receiving them are the six acts (prescribed) for a Brahmana.
10.76. But among the six acts (ordained) for him three are his means of subsistence, (viz.) sacrificing for others, teaching, and accepting gifts from pure men.
10.80. Among the several occupations the most commendable are, teaching the Veda for a Brahmana, protecting (the people) for a Kshatriya, and trade for a Vaisya.
But, when unable to maintain himself and the family by doing the above alone, or in times of emergency, a Brahmin can adopt the occupations prescribed for the Kshatriyas or for the Vaishyas without committing sin.
10.81. But a Brahmana, unable to subsist by his peculiar occupations just mentioned, may live according to the law applicable to Kshatriyas; for the latter is next to him in rank.
10.82. If it be asked, ’How shall it be, if he cannot maintain himself by either (of these occupations?’ the answer is), he may adopt a Vaisya’s mode of life, employing himself in agriculture and rearing cattle.
10.83. But a Brahmana, or a Kshatriya, living by a Vaisya’s mode of subsistence, shall carefully avoid (the pursuit of) agriculture, (which causes) injury to many beings and depends on others
But there are still some restrictions in place and if a Brahmin indulges in these forbidden occupations then he incurs a sin of loss of caste.
10.92. By (selling) flesh, salt, and lac a Brahmana at once becomes an outcast; by selling milk he becomes (equal to) a Sudra in three days.
10.93. But by willingly selling in this world other (forbidden) commodities, a Brahmana assumes after seven nights the character of a Vaisya.