SB 9.16.12
yacyamanah krpanaya
rama-matratidarunah
prasahya sira utkrtya
ninyus te ksatra-bandhavah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
With pitiable prayers, Renuka, the mother of Parasurama and wife of Jamadagni, begged for the life of her husband. But the sons of Kartaviryarjuna, being devoid of the qualities of ksatriyas, were so cruel that despite her prayers they forcibly cut off his head and took it away.