Auth::attempt() return false always

alaways returning false values but values are coming correct through $request what should I do?

    public function login(Request $request)
    {
        $email = $request->input('email');//singh@gmail.com
        $password = $request->input('password');//a

        //$input = ['email'=>$email,'password'=>$password];

        if (Auth::attempt(['email'=>'singhkulpreet05@gmail.com','password'=>$password])) {
            return "logged in";
        }
        else return "notttt";
    }

via Chebli Mohamed