SB 8.9.25

cakreṇa kṣura-dhāreṇa
 jahāra pibataḥ śiraḥ
haris tasya kabandhas tu
 sudhayāplāvito ’patat
Synonyms: 
cakreṇa — by the disc; kṣura-dhāreṇa — which was sharp like a razor; jahāra — cut off; pibataḥ — while drinking nectar; śiraḥ — the head; hariḥ — the Supreme Personality of Godhead; tasya — of that Rāhu; kabandhaḥ tu — but the headless body; sudhayā — by the nectar; aplāvitaḥ — without being touched; apatat — immediately fell dead.
Translation: 
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.
Purport: 

When the Personality of Godhead, Mohinī-mūrti, severed Rāhu’s head from his body, the head remained alive although the body died. Rāhu had been drinking nectar through his mouth, and before the nectar entered his body, his head was cut off. Thus Rāhu’s head remained alive whereas the body died. This wonderful act performed by the Lord was meant to show that nectar is miraculous ambrosia.