From:

Child, Francis James. The English and Scottish Popular Ballads, Part IX. Boston: Houghton, Mifflin and Co, 1894, page 203, in the appendix chapter "Fragments":

It was far in the night, and the bairnies grat;
The mither beneath the mools heard that.

sung in Wuthering Heights, ch. 9, has not unnaturally been taken for a relic of a traditional Scottish ballad of a dead mother returning to her abused children. It is, in fact, a stanza (not literally well remembered) from the Danish ballad 'Moderen under Mulde,' Grundtvig, II, 470, No 89, B 11, translated by Jamieson, and given in the notes to the fourth canto of Scott's Lady of the Lake.

A longer excerpt is given in

Tait, William, and C. I. Johnstone. Tait's Edinburgh Magazine, Vol X (1843). Edinburgh: William Tait.

It was far in the night, and the bairnies grat,
Their mither aneath the mools heard that;
The wife stood up at our Lord's knee,
And said, 'O! may I gang my bairnies to see!'
She pleaded sae sair, and she pleaded sae lang,
That he at last gied her leave to gang.
'But see ye come back ere the cock does craw,
For langer ye mauna bide awa.'