Full Idea
It is always false to say that all our notions come from the so-called external senses, for the notion I have of myself and of my thoughts, and consequently of being, substance, action, identity, and many others, come from an internal experience.
Gist of Idea
Knowledge doesn't just come from the senses; we know the self, substance, identity, being etc.
Source
Gottfried Leibniz (Discourse on Metaphysics [1686], §27)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.37
A Reaction
Of course, an empiricist like Hume would not deny this, as he bases his views on 'experience' (including anger, for example), not just 'sense experience'. But Hume, famously, said he has no experience of a Self, so can't get started on Leibniz's journey.