Lucifer was indeed an angel of his word. He did not approve of the idea of leaving his one true vessel in the hands of a demon, but Lucifer was well aware that Ruby would never willingly harm Sam Winchester. She cared for him, something that most of his demons were far from capable of. Because of the love that she held for the man that he wore, Lucifer trusted that she would protect his vessel. She would keep it safe, she would keep it hidden, and she would spend hours pretending that, perhaps, Sam Winchester still remembered her. He did. Lucifer knew that, easily. It was merely a matter of getting Sam to take control of those memories. To take control of anything, seeing as he spent most of his time curled away in silence. When Sam did choose to surface, Lucifer was hardly a concern for the human. He occupied his mind with twisted delusions and fantasies. Dean was with him. He was safe.
Obviously, Sam was insane.
"I suppose I did," Lucifer replied, appearing behind Ruby without warning. The house that he had picked for this particular event was fairly nice compared to that of the ruins that surrounded them. It was clean, undamaged, and happened to have more electricity than a handful of people could scrape together nowadays. There was food in the kitchen, should Sam require a meal or two, and the outside was - as Lucifer had warned Ruby - securely guarded. If Ruby did try to pull something, they would stop her. She wouldn't get away.
"Keep him here," Lucifer said, walking across the room to pick up one of the books settled on a small table. The bible. Ha. He flipped it open to Revelations, then turned back to look at Ruby once more. "Make him comfortable."
Lucifer would tend to business from above. He wouldn't be able to make much contact, but he would be able to watch things easily enough while Ruby enjoyed her reward. "Twenty-four hours, Ruby. That's all you get. Are we clear?"