Manava Dharmashastra 11.128

11.128

tryabdaṃ cared vā niyato jaṭī brahmahaṇo vratam
vasan dūratare grāmād vṛkṣamūlaniketanaḥ //

But if a Brahmana unintentionally kills a Kshatriya, he shall give, in order to purify himself, one thousand cows and a bull;