This is a Southwest US Hispanic Christmas folksong whose title is given as "Duérmete, Niño lindo" (the incipit) or "A la ru" (from the refrain). The usual English version is "Oh, sleep now, holy baby" by John Donald Robb [d. 1989] (but note that the Spanish Infant is "pretty", not "holy".

Duérmete, Niño lindo

1. Duérmete, Niño lindo, en los brazos del amor
   mientras que duerme_y descansa la pena de mi dolor.
   
             (Estribillo:)
        A la ru, a la mé, a la ru, a la mé,
        a la ru, a la mé, a la ru, a la ru, a la mé.
2. No temas al rey Herodes que nada te_ha de hacer;
   en los brazos de tu y_ahi nadie te_ha de_ofender.
             (Estribillo:)
        A la ru, a la mé, a la ru, a la mé,
        a la ru, a la mé, a la ru, a la ru, a la mé.

Here's the MIDITEXT of the melody line:

MIDI file: alaru.mid

Timebase: 192

Name: A La Ru
Text: By novmeksikia popolmelodio Kristnaska
Copyright: anonima
Tempo: 076 (789473 microsec/crotchet)
Key: D
TimeSig: 6/8 24 8
Start
0000 1 69 110 0094 0 69 000 0002 1 74 110 0160 0 74 000 0032 1 74 110 0094 0 74 000 0002 1 73 110 0096 0 73 000 0000 1 71 110 0094 0 71 000 0002 1 73 110 0094 0 73 000 0002 1 74 110 0094 0 74 000 0002 1 69 110 0286 0 69 000 0002 1 74 110 0094 0 74 000 0002 1 73 110 0094 0 73 000 0002 1 71 110 0160 0 71 000 0032 1 71 110 0094 0 71 000 0002 1 66 110 0096 0 66 000 0000 1 64 110 0094 0 64 000 0002 1 62 110 0094 0 62 000 0002 1 66 110 0448 0 66 000 0032 1 66 110 0094 0 66 000 0002 1 66 110 0094 0 66 000 0002 1 66 110 0094 0 66 000 0002 1 66 110 0094 0 66 000 0002 1 66 110 0094 0 66 000 0002 1 64 110 0094 0 64 000 0002 1 62 110 0094 0 62 000 0002 1 66 110 0160 0 66 000 0032 1 66 110 0190 0 66 000 0098 1 71 110 0094 0 71 000 0002 1 69 110 0160 0 69 000 0032 1 69 110 0094 0 69 000 0002 1 67 110 0096 0 67 000 0000 1 66 110 0094 0 66 000 0002 1 64 110 0094 0 64 000 0002 1 62 110 0256 0 62 000 0128 1 69 110 0094 0 69 000 0002 1 69 110 0094 0 69 000 0002 1 71 110 0096 0 71 000 0000 1 67 110 0160 0 67 000 0128 1 71 110 0094 0 71 000 0002 1 71 110 0094 0 71 000 0002 1 69 110 0096 0 69 000 0000 1 66 110 0160 0 66 000 0128 1 69 110 0094 0 69 000 0002 1 69 110 0094 0 69 000 0002 1 67 110 0096 0 67 000 0000 1 64 110 0160 0 64 000 0032 1 69 110 0160 0 69 000 0032 1 67 110 0094 0 67 000 0002 1 66 110 0256 0 66 000 0128 1 69 110 0094 0 69 000 0002 1 69 110 0094 0 69 000 0002 1 71 110 0096 0 71 000 0000 1 67 110 0160 0 67 000 0128 1 71 110 0094 0 71 000 0002 1 71 110 0094 0 71 000 0002 1 69 110 0096 0 69 000 0000 1 66 110 0160 0 66 000 0128 1 62 110 0094 0 62 000 0002 1 64 110 0094 0 64 000 0002 1 66 110 0094 0 66 000 0002 1 67 110 0094 0 67 000 0002 1 66 110 0094 0 66 000 0002 1 64 110 0094 0 64 000 0002 1 62 110 0094 0 62 000 0002 1 64 110 0094 0 64 000 0002 1 62 110 0448 0 62 000
End

This program is worth the effort of learning it.

To download the latest version of MIDItext and get instructions on how to use it click here

ABC format:

X:1
T:A La Ru
M:6/8
Q:1/4=76
K:D
Ad2dcB|cdA3d|cB2BFE|DF5|FFFFFE|DF2F3|BA2AGF|
ED4A|ABG3B|BAF3A|AGE2A2|GF4A|ABG3B|BAF3D|
EFGFED|ED37/8||

I believe the copyright to the Robb translation, which follows, is held by the (© 1954) University of New Mexico Press, as is that to Mr. Robb's arrangement, which can be found in several recent US hymnals, including the 1990 Presbyterian Hymnal (also published under the title Hymns, Psalms and Spiritual Songs) and the 1995 Lutheran supplement With One Voice:

Oh, Sleep Now, Holy Baby

1. Oh, sleep now, holy baby, with you head against my breast;
   - meanwhile the pangs of my sorrow are soothed and put to rest.
             (Refrain:)
        A la ru, a la mé, a la ru, a la mé,
        a la ru, a la mé, a la ru, a la ru, a la mé.
2. You need not fear King Herod, he will bring no harm to you;
   so rest in the arms of your mother who sings you a la ru.
             (Estribillo:)
        A la ru, a la mé, a la ru, a la mé,
        a la ru, a la mé, a la ru, a la ru, a la mé.