摩訶止觀 6.65

6.65

若明一切法如鏡中像，見不可見。見，是亦有；不可見，是亦無。雖無而有，雖有而無。如是觀者能破諸法見思，成惑智、因果無生，是名亦空亦有門破假觀之意也。

If one explains that all dharmas are like an image in a mirror, seen yet invisible: being seen is also existence; being invisible is also non-existence. Although non-existent, it exists; although existent, it is non-existent. One who contemplates like this can break the views and thoughts of dharmas, bringing about the non-arising of delusion, wisdom, cause, and effect; this is called the purpose of the contemplation breaking down the provisional through the gate of both emptiness and existence.