In which reference can I find a definition for the equivalence of DFAs? How is the equivalence of DFA defined?  I found the equivalence of states --- James Hein, section 5.3, page 301.  But he doesn't define equivalence between entire automata.  (Ullman and Hopcropft seem to define neither.)
You can find a definition in Automata Theory, Languages and Computation by Hopcroft, Motwani, Ullman, in the fourth chapter.

Here's a link : HMU, the section begins at page 171 of the pdf

Two DFA are said to be equivalent if they accept the same language, and (an equivalent proposition) if they have the same minimal automaton (which is unique).