Marry in haste, repent at leisure

This proverbial saying was first expressed in print by William Congreve in his comedy of manners The Old Batchelour, 1693:

Thus grief still treads upon the heels of pleasure:
Married in haste, we may repent at leisure.

Congreve took his lead from Shakespeare who had previously coined who wooed in haste, and means to wed at leisure, which conveys much the same idea.

Both authors were expressing the notion that, while courtships and weddings are brief, marriages are longlasting – giving plenty of time to muse on the wisdom of a rushed alliance.