Is it permissible to pray behind a sitting person whose back screens the worshipper?

There is no harm in praying behind a sitting person who has his back to you. Rather, it is disliked to pray facing a person's face if that will distract the worshipper. The proof for this is the actions of Omar ibn al-Khattab and Uthman ibn Affan, may Allah be pleased with them, and what was narrated from Aisha, may Allah be pleased with her, that the Prophet, peace and blessings be upon him, used to pray in line with the bed while she was lying between him and the Qiblah. As for the sitting person who has his back turned and does not move or distract the worshipper, there is no harm in praying behind him, just as there is no harm in praying towards a sleeping person, based on what Aisha, may Allah be pleased with her, narrated that she used to sleep in front of the Prophet, peace and blessings be upon him, with her legs in his Qiblah, and when he prostrated, he would nudge her, and she would draw up her legs, and when he stood up, she would extend them.