Hazrat Nafi' narrates that when Hazrat Ibn Umar (may Allah be pleased with them) could not find any pillar in the mosque for sutrah, he would tell me to sit with your back towards me.

Hazrat Qatadah says that if a person is sitting, then someone praying behind him can make him his sutrah.

Hasan says that a person can serve as a sutrah for the one who is praying. And Ibn Sirin says that a person cannot serve as a sutrah for the one who is praying.

Hazrat Nafi' narrates that Hazrat Ibn Umar (may Allah be pleased with them) would seat a man in front of him and pray behind him, while people would continue to pass in front of that man.

Hazrat Hammad says that I asked Ibrahim whether a sleeping person can be made a sutrah. He said no. I asked whether a sitting person can be made a sutrah. He said yes.