I don't know what the original song is unless its that by Colley Cibber in his ballad opera 'Flora', 1729, but the simplified tune there had already been printed under Scots and Irish Gaelic titles. Cibber's song commences" 'Twas past twelve o'clock on a fine summer morning". Robert Burns had a hand in fitting verses to the tune in 'The Scots Musical Museum', #227 (1790), and his song starts: 'Twas past ane o clock in a cauld frosty morning". Just how much of the song is by Burns seems to be unknown. For many copies of the tune under English and Gaelic titles see "I am asleep and don't waken me" in the Irish tune index on my website. [A late song by Hector MacNeill, "Jeannie's Black E'ne" uses the Gaelic title as the burden of his verses. It's in the Scarce Songs 1 file on my website, listed in Mudcat's Links.]