The Supreme Personality of Godhead, Hari, using His disc, which was sharp like a razor, at once cut off Rāhu’s head. When Rāhu’s head was severed from his body, the body, being untouched by the nectar, could not survive.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
चक्रेण क्षुरधारेण जहार पिबतः शिरः । हरिस्तस्य कबन्धस्तु सुधयाऽऽप्लावितोऽपतत्
cakreṇa kṣuradhāreṇa jahāra pibataḥ śiraḥ | haristasya kabandhastu sudhayā''plāvito'patat
SB 8.9.25