APAD: It never rains but it pours

'It never rains but it pours'?

       When troubles come they come together.

What's the origin of the phrase 'It never rains but it pours'?

A proverbial phrase. The origin is unknown but the phrase has been in use since the early 18th century; for example, this item from a work by John Arbuthnot, 1726:

  It cannot rain but it pours; or London strow'd with rarities.