I had the same issue. The reason for mine was that I defined setPasswordAttribute in my Usermodel so every time, I enter plain password, it hashes before sending to DB.

public function setPasswordAttribute($password)
{
$this->attributes['password'] = Hash::make($password);
}

and in my db:seed, I was creating a user with hashed password with Hash::make("password"), too. So laravel hashes hashed password
In laravel version 5.* you don't need to hash input password for Auth, because Auth manages it itself. you just have to pass {{csrf_field()}} through form.

Böyle bir kaynak buldum yardımcı olabilir.