Manusmriti
इयं विशुद्धिरुदिता प्रमाप्याकामतो द्विजम् । कामतो ब्राह्मणवधे निष्कृतिर्न विधीयते ॥ ८९ ॥
This expiation has been prescribed for unintentionally killing a Brahmana; but for intentionally slaying a Brahmana no atonement is ordained.
english translation
iyaM vizuddhiruditA pramApyAkAmato dvijam । kAmato brAhmaNavadhe niSkRtirna vidhIyate ॥ 89 ॥
hk transliteration by Sanscript