Srimad-Bhagavatam: Canto 7 - Chapter 1 - Verse 10
द्रव्ययज्ञैर्यक्ष्यमाणं दृष्ट्वा भूतानि बिभ्यति ।एष माकरुणो हन्यादतज्ज्ञो ह्यसुतृप्ध्रुवम् ॥ १० ॥
dravya-yajñair yakṣyamāṇaṁdṛṣṭvā bhūtāni bibhyatieṣa mākaruṇo hanyādataj-jño hy asu-tṛp dhruvam
Upon seeing the person engaged in performing the sacrifice, animals meant to be sacrificed are extremely afraid, thinking, “This merciless performer of sacrifices, being ignorant of the purpose of sacrifice and being most satisfied by killing others, will surely kill us.”
Animal sacrifice in the name of religion is current practically all over the world in every established religion. It is said that Lord Jesus Christ, when twelve years old, was shocked to see the Jews sacrificing birds and animals in the synagogues and that he therefore rejected the Jewish system of religion and started the religious system of Christianity, adhering to the Old Testament commandment “Thou shalt not kill.” At the present day, however, not only are animals killed in the name of sacrifice, but the killing of animals has increased enormously because of the increasing number of slaughterhouses. Slaughtering animals, either for religion or for food, is most abominable and is condemned herein. Unless one is merciless, one cannot sacrifice animals, either in the name of religion or for food.