Yogasutra 4.15

4.15

vastusāmye cittabhedāt tayor vibhaktaḥ panthāḥ ||

Since perception and desire vary with regard to the same object, mind and object are of different nature.

That is, there is an objective world independent of our minds. This is a refutation of Buddhistic Idealism. Since different people look at the same thing differently, it cannot be a mere imagination of any particular individual.