Error "Call to undefined method Illuminate\Auth\GenericUser" when accessing to hasMany relationship of Auth::user()

I defined a relationship One-to-Many between User and Patient, but when I try to save a new patient record with the authenticated user I get the error

Call to undefined method Illuminate\Auth\GenericUser::patients()

Here are my tables:

// Users table
Schema::create('users', function (Blueprint $table) {
    $table->increments('id');
    $table->string('name');
    $table->string('email')->unique();
    $table->string('password', 60);
    $table->rememberToken();
    $table->timestamps();
    $table->softDeletes();
});

// Patients table
Schema::create('patients', function (Blueprint $table) {
    $table->increments('id');
    //Foreign key
    $table->integer('user_id')->unsigned();
    $table->string('ci')->unique();
    $table->string('name');
    $table->string('last_name');
    $table->string('gender');
    $table->date('birth_date')->nullable();
    $table->string('place')->nullable();
    $table->timestamps();
    $table->softDeletes();

    $table->foreign('user_id')
          ->references('id')->on('users');
});

In PatientController I call Auth::user() to save a new patient:

public function store(PatientRequest $request){
    $patient = new Patient($request->all());
    Auth::user()->patients()->save($patient);
    $last = Patient::get()->last();

    return redirect()->route('patient.histories.create', [$last->id])->with('message', 'Success!');
}

And the relationships are defined as follows:

// IN USER MODEL
public function patients(){
    return $this->hasMany('App\Patient');
}

// IN PATIENT MODEL
public function user(){
    return $this->belongsTo('App\User');
}

At this point I really don't know what is wrong, but when I create a new patient record from tinker it works as expected:

>>> $patient = new App\Patient;
>>> $patient->ci = "1234567";
.......
.......

>>> $user = App\User::first();
>>> $user->patients()->save($patient);

Can someone spot where is the error, please?

via Chebli Mohamed