Origins to Away in a Manger stretch back to 1865. It's one of those toons with a cloudy past. It's usually attributed as "American Anonymous". But some attributes to it are listed as follows:

First published by James R. Murray in a Lutheran Sunday School book in 1865.

Author of the first two stanzas unknown.

There are at least two common melodies for the song, one in Britain, one commonly found in the USA.