Sources? Not as much. But i mean, thats the whole basis of science. It assumes an ordered universe. It also confirms its existence. Every time you pop an aspirin you're downing a pill created through a complex chemical process that occurs the same way each time (barring mistakes on the factory), and every time you check your GPS you're listening to the directions of a machines that assumes physics has never and will never change.

The universe obeys the laws of physics and physics follows mathematical order readily and frequently observed, described, and used by scientists. The proof of an ordered universe is that science works at all.

As others have mentioned, quantum physics may be an exception to this rule, but on any greater scale, your inability to predict where every raindrop will fall isn't due to randomness in the way rain falls, but because you have neither a supervomputer nor an exact map of the conditions of the atmosphere within and around the cloud. If you did you could predict when a drop would precipitate and from there what its trajectory would be until it hit the ground.