Let A, B, C be topological spaces and let u:A→B, v:B→C be continuous mappings; put w=v∘u. Let E and E′ be C-spaces. The canonical morphism from MorC(E;E′)A into MorA(EA;EA′) is the composite morphism of the morphism MorC(E;E′)A→MorB(EB;EB′)A deduced from the canonical morphism of MorC(E;E′)B into MorB(EB;EB′) and the canonical morphism of MorB(EB,EB′)A into MorA(EA,EA′).
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.