If we're talking Scottish versions of the song which begin I must away love, then I expect most people will be familiar with it from the arrangement recorded by the Tannahill Weavers. I don't know if they credited their source or not; it isn't difficult to find transcriptions of their recording on the web, but nobody seems to have bothered to quote the sleevenotes. Stanley Robertson and Bobby Robb are both possible traditional sources. Robb's set is quoted in Shelia Douglas' book Come Gie's a Sang; you can see Robertson's text at Nathan D. Rose's site: I Must Away, Love

Note that Nathan, who recorded that text from Stanley, asks that it not be reproduced on other websites.