There are numerous times that Juliet's death is foreshadowed. I think you need to be more specific in your question but I believe the following information may help you:
1. At the Capulet feast
Juliet says, "If he be married./ my grave is like to be my wedding bed" (1.5.135)
She means that if Romeo is married, she will die unmarried, because she will never marry another, but she is also unkowningly foreshadowing her fate, in which her grave does become her wedding bed.
2. When Juliet learns that Romeo has been banished she says, "I'll to my wedding-bed; / And death, not Romeo, take my madienhead!" (3.2.136-137)
Friar Laurence also alludes to it as stated in the answer below.
In the play 'Romeo and Juliet' by William Shakespeare, Juliet's death (and the tragic fate of both) are foreshadowed several times. Do you mean the part where Friar Laurence alludes to the calamitous events that will befall Juliet, as 'wedded to ' him? If so, the right words would be the quote where the friar says to Romeo 'affliction is enamor'd of thy parts,And thou art wedded to calamity' in Act 3 Scene 111. By this, the friar means that calamity is awaiting Juliet, and Fate has nothing but bad luck in store for both of them - they are 'star-cross'd'. Affliciton refers to the affliction or curse of bad luck (if you remember, Romeo has had a bad run of it recently Rosaline,then loving an emeny's daughter,then losing Mercutio,killing Tybalt, being banished) and the friar is commiserating with him.