It is narrated from Hazrat Jabir (may Allah be pleased with him) that I saw the Prophet (peace and blessings be upon him) delivering the sermon while standing, then he would sit for a short while and would not speak to anyone, then he would stand up and deliver the second sermon. Therefore, if any of you says that he saw the Prophet (peace and blessings be upon him) delivering the sermon while sitting, do not confirm it.
Hadith Referenceمسند احمد / أول مسند البصريين / 20919
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن