SB 9.16.11
drstvagny-agara asinam
avesita-dhiyam munim
bhagavaty uttamasloke
jaghnus te papa-niscayah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The sons of Kartaviryarjuna were determined to commit sinful deeds. Therefore when they saw Jamadagni sitting by the side of the fire to perform yajña and meditating upon the Supreme Personality of Godhead, who is praised by the best of selected prayers, they took the opportunity to kill him.