SB 1.7.35
mainam partharhasi tratum
brahma-bandhum imam jahi
yo ’sav anagasah suptan
avadhin nisi balakan
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Lord Sri Krsna said: O Arjuna, you should not show mercy by releasing this relative of a brahmana [brahma-bandhu], for he has killed innocent boys in their sleep.
Purpor by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupadat:
The word brahma-bandhu is significant. A person who happens to take birth in the family of a brahmana but is not qualified to be called a brahmana is addressed as the relative of a brahmana, and not as a brahmana. The son of a high court judge is not virtually a high court judge, but there is no harm in addressing a high court judge’s son as a relative of the honorable justice. Therefore, as by birth only one does not become a high court judge, so also one does not become a brahmana simply by birthright but by acquiring the necessary qualifications of a brahmana. As the high court judgeship is a post for the qualified man, so also the post of a brahmana is attainable by qualification only. The sastra enjoins that if good qualifications are seen in a person born in a family other than that of a brahmana, the qualified man has to be accepted as a brahmana, and similarly if a person born in the family of a brahmana is void of brahminical qualification, then he must be treated as a non-brahmana or, in better terms, a relative of a brahmana. Lord Sri Krsna, the supreme authority of all religious principles, the Vedas, has personally pointed out these differences, and He is about to explain the reason for this in the following slokas.