I have a fairy by my side
Which says I must not sleep,
When once in pain I loudly cried
It said "You must not weep"
If, full of mirth, I smile and grin,
It says "You must not laugh"
When once I wished to drink some gin
It said "You must not quaff".

When once a meal I wished to taste
It said "You must not bite"
When to the wars I went in haste
It said "You must not fight".

"What may I do?" at length I cried,
Tired of the painful task.
The fairy quietly replied,
And said "You must not ask".

Moral: "You mustn't."