Neither. The dirt will fall off itself eventually. Just kidding
This question brought memories of how my grandma washed me in a village in Ukraine without running water when I was little. She would first pour cold water into a large bοwl, then pour boiling water to mix in. Then get me into that bowl and use Marseille soap (see the Wikipedia, but instead of being made of vegetable oil, it was made of animal fats). Often she wouldn't get the cold/scorching hot mixture right. So, it was not my favorite thing to do.