Yogācārabhūmi-śāstra: Volume 34 (34)

Thus, all these external phenomena. The first six are the things that are apprehended. The last ten are the requisites for the body. In summary, one should know that their nature is all impermanent. Why? Because the transformation of form and appearance can be presently observed. As previously stated, and so on.

Thus, all these external phenomena: the first six are things apprehended by the five aggregates, and the last ten are requisites for the body. In summary, the nature of these dharmas is all impermanent. Why is that? Because the transformation of the form and appearance of these dharmas can be presently observed, as previously stated in detail.