Mbh 12.78.8b

Manu himself has said that those heroes repair to the region of Brahman. As persons become cleansed of all their sins by undergoing the final bath on a horse-sacrifice even so they that die at the edge of weapons while fighting wicked people, become cleansed of their sins. Righteousness becomes unrighteousness, and unrighteousness becomes righteousness, according to place and time. Such is the power of place and time (in determining the character of human acts). The friends of humanity, by doing even acts of cruelty, have attained to high heaven. Righteous Kshatriyas, by doing even sinful acts, have attained to blessed ends.[235] The Brahmana, by taking up arms on these three occasions, does not incur sin, viz., for protecting himself, for compelling the other orders to betake themselves to their duties, and for chastising robbers."