उत्त्वा॑ मंदंतु॒ स्तोमाः॑ कृणु॒ष्व राधो॑ अद्रिवः । अव॑ ब्रह्म॒द्विषो॑ जहि ॥ प॒दा प॒णीँर॑रा॒धसो॒ नि बा॑धस्व म॒हाँ अ॑सि ।न॒हि त्वा॒ कश्च॒न प्रति॑ ॥
Rig Veda 8.64.1-2: May our hymns please you; O lord of resolute will power, please display your bounty. May you drive off the Panis. May you crush with your foot the niggard churls who offer no homage. You are powerful; there is none so powerful as you are.
Who are panis and why Vedas are asking them to kill? Is it justified.
This is a reference from Rigveda 10.108 (mandala 10 sukta 108). From those reference, it is found that Pani is a group of demons (Asuras) kidnap the cattle of Angirasas (sons of sage Angiras). They hide those cows in a cave. Then Sarama is described to have found the cows by the path of truth. There is no such proof in Vedas about their sacrifice. This can be the misinterpretation of of the vedic texts.
Here are some references from the internet which can be used for more reference. Speaking Tree, Wikipedia - Panis, Wikipedia - Sarama
All further addition/correction to the topic are welcome.
