It is narrated from Abu Huraira (may Allah be pleased with him) that the Prophet (peace be upon him), Abu Bakr, Umar, and Uthman (may Allah be pleased with them) used to deliver two sermons on the pulpit on Friday, and they would separate the two sermons by sitting in between, until Muawiyah (may Allah be pleased with him) delivered the first sermon while sitting and the second sermon while standing.
Hadith Referenceمسند الإمام الشافعي / كتاب الجمعة / 438