Thomas Legler, officer in the 1er régiment Suisse.
His recollections (written in German) of 1812:
And of 1814 and 1815:
On the morning of 29 November 1812, his commander asked lieutenant Legler to sing a song to him, which he had sung some times before: "Unser Leben gleicht der Reise ..." (our live resembles the voyage of a wanderer in the night). A hundred years later, this song became famous as the "Beresina-Lied", popular legend wanted it to have been sung by all the Swiss soldiers at the Beresina.
Some more info about the song here (in French):