Corollary (Schur’s lemma)
Tag 00RZ, permanent. Cite it as [Bourbaki, Tag 00RZ].
Algebra, VIII, p. 47, § 3. Simple Modules
The endomorphism ring of a simple module is a field.
If M is a simple A-module, then every nonzero element of the nonzero ring End is invertible (Proposition 2, c)), so End is a field.
Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.