AULD LANG SYNE.

In a letter to Mr Thomson, dated September 1793, Robert Burns wrote:

One more song have I done: "Auld Lang Syne". The air is but mediocre; but the following song, the old song of the olden times, and which has never been in print, nor even in manuscript, until I took it down from an old man's singing, is enough to recommend any air.

Source:
The National Burns, vol.II, edited by Rev George Gilfillan, published by William Mackenzie (no publication date - possibly early 1900s).