Proposition 3
Tag 060E, permanent. Cite it as [Bourbaki, Tag 060E].
Algebra, chapter III, § 4. Tensor products of algebras
Let be two commutative rings, a ring homomorphism and two -algebras. Then the canonical -module isomorphism
(II, § 5, no. 1, Proposition 3) is a -algebra isomorphism.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.