It's probably wrong but I grew up knowing it went like this

Hush little baby don't say a word
Cause daddy's gonna buy you a mocking bird
And if that mocking bird don't sing
Then daddy's gonna but you a diamond ring
And if that diamond ring is made out of brass
Then daddy's gonna buy you a looking glass
And if that looking glass don't shine
Then daddy's gonna buy you a valentine
And if that valentine not red
Daddy's gonna buy you a brass bed
And if that brass bed gets broke
Then daddy's gonna buy you a Billy goat
And if that Billy goat falls down
Well you're still the greatest baby in this whole darn town
So hush little baby if you don't
Daddy's gonna buy you a mocking bird.