Valmiki Ramayana Ayodhya Kanda Sarga 21 Shloka 31

पूर्वम् earlier, अस्माकम् in our, कुले च race, पितुः of father, सगरस्य Sagara's, आज्ञया by command, भूमिम् earth, खनद्भि: by those excavating, सागरैः by the sons of Sagara, सुमहान् very great (fearful), वधः slaughter, आवाप्तः was met with.

Earlier the sons of Sagara, born in our family, while excavating the earth by the order of their father met a terrible death.