String email = emailEditText.getText().toString();
String password = emailEditText.getText().toString();

fbUsers.orderByChild("email").equalTo(email).limitToFirst(1).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        HashMap<String, User> usersHashMap = (HashMap<String, User>) dataSnapshot.getValue();

        Map.Entry<String, User> firstEntry = usersHashMap.entrySet().iterator().next();
        User foundUser = firstEntry.getValue();

        Log.d("Login: ", foundUser.getEmail());
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

public class User {
    private String email;
    private String password;

    User() {}

    public User(String email, String password) {
        this.email = email;
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}