Quotes on fate

Hi there,

I've been wracking my brain to remember the wording, but I recall a passage that I think is from

Shakespeare, but may be from Classical Theatre as well, or not, I'm really starting to question my own memory. It has to do with something like (and this is very paraphrasy) "do not seek to know your fate, you have enough misery in the present to add the future to it, it is a sorrow too soon given" or something like that.

Does this sound familiar to anyone? If so, any idea whence it comes?

Thanks

G