Śrīmad-Bhāgavatam · Text 10.54.40
Who is speaking and story frame
क्षत्रियाणामयं धर्म: प्रजापतिविनिर्मित: ।
भ्रातापि भ्रातरं हन्याद् येन घोरतमस्तत: ॥ ४० ॥
kṣatriyāṇām ayaṁ dharmaḥ
prajāpati-vinirmitaḥ
bhrātāpi bhrātaraṁ hanyād
yena ghoratamas tataḥ
[Turning to Rukmiṇī, Balarāma continued:] The code of sacred duty for warriors established by Lord Brahmā enjoins that one may have to kill even his own brother. That is indeed a most dreadful law.
Read the purport on Vedabase.ioFrom Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.