Ibrahim bin Ubaid reports: I went to the service of Sayyiduna Jabir bin Abdullah (may Allah be pleased with him), and found him leading his companions in prayer while sitting. When he finished the prayer, I asked him about this. He said: "I am actually unable to stand. When you pray behind me, then perform the prayer sitting," because I heard the Prophet Muhammad (peace be upon him) say: "The Imam is a shield; if he prays standing, then you should also pray standing, and if he prays sitting, then you should also pray sitting."
Hadith Referenceسنن الدارقطني / كتاب الصلاة / 1564
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 1564، ((وعبد بن حميد فى المنتخب من مسنده))، 1152، وأورده ابن حجر فى ((المطالب العالية))، 413، 413، 630»