The same thing, from the Silmarillion:

The love of Finwë and Míriel was great and glad, for it began in the Blessed Realm in the Days of Bliss. But in the bearing of her son Míriel was consumed in spirit and body; and after his birth she yearned for release from the labour of living. And when she had named him, she said to

Finwë: ‘Never again shall I bear child; for strength that would have nourished the life of many has gone forth into Fëanor.’

[They try to heal her and even the gods fail at it]

‘It is indeed unhappy,’ said Míriel, ‘and I would weep, if I were not so weary. But hold me blameless in this, and in all that may come after.’

She went then to the gardens of Lórien and lay down to sleep; but though she seemed to sleep, her

spirit indeed departed from her body, and passed in silence to the halls of Mandos.