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 only while standing.
Hadith Referenceمسند احمد / أول مسند البصريين / 21051
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن