Valmiki Ramayana Bala Kanda Sarga 23 Shloka 14

राघव O Rama, तदाप्रभृति from that time onwards, अनङ्ग इति as Ananga, विख्यात: had become wellknown, यत्र where, अङ्गम् body, प्रमुमोच ह he gave up, स:च that place, श्रीमान् beautiful, अङ्गविषय: Ananga desa, विख्यात: famed.

O descendant of the Raghus, from that time onwards, he was known as 'Ananga' (one without form). The beautiful place where he gave up his body is known as Angadesa.