A-wassail, a-wassail throughout all this town,
Our cup it is white and our ale it is brown.
Our wassail is made of good ale and cake,
Some nutmeg and ginger, it's the best we could

Fol-dee-dol, lol-dee-dol-dee-dol,
Lol-dee-dol-dee-dol, lol-dee-dol-dee-
Fol-dee-derol, lol-dee-der-
Sing too-ra-li-doh.

Our wassail is made of an el'berry bough,
Although, my good neighbour, we'll drink unto thou,
Besides all on earth, we have apples in store,
Pray let us come in, for 'tis cold by the door.

We know by the moon that we are not too soon,
And we know by the sky that we are not too high.
We know by the stars that we are not too far,
And we know by the ground that we are within sound.

Now, master and mistress, thanks to you we'll give,
And for our jolly wassail as long as we live.
And if we should live till another New Year,
Perhaps we may call and see who do live here.

"We end as we begin with a wassail song, sung from house to house at mid-winter, for luck. The wassailers, perhaps five or six of them, carried a wooden bowl decorated with holly and ivy. in which to collect money or bread and cheese or beer, in return for the good luck wishes conveyed by their song. Sometimes they carried a be-ribboned elder bough as an emblem of their standing as luck-bringers. Many wassail songs indicate that in the past the reception of the luck-visitors was a ceremonious affair, with the person who gave them entry dressed in her best, wearing a silver pin or carrying a golden mace." (A.L. Loyd from the liner notes of The Watersons album "Frost and Fire" source)
Growing up with the carol, Gower-born Phil Tanner came to introduce it to the world via a 1937 recording released on 78rpm record. For more discussion about the history of this traditional Welsh folk song, head over to the expansive database of all things tradition, Mudcat.