Proposition 2
Tag 094R, permanent. Cite it as [Bourbaki, Tag 094R].
Integration, chapter V, § 6. Images of a measure
— For every numerical function defined on X,
(2)
This follows from Th. 1 of §4, No. 2.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.