Green’s Dictionary of Slang

ally-beg n.

[? according to B&L Gaelic aille, pleasant + beg, little (place); thus a pleasant little place]

a comfortable bed.

1889–90

Barrère & Leland Dict. of Sl., Jargon and Cant I 33/2: Ally-beg, a bed. This very ancient and obsolete cant word [etc.].