The Messenger of Allah ﷺ used to deliver two sermons on Friday, sitting once between them.
حدثنا أزهر بن القاسم حدثنا عبد الله عن نافع
أن رسول الله ﷺ كان يخطب خطبتين يوم الجمعة يجلس بينهما مرة
Its isnad is sahih. Azhar bin Qasim Rasibi Basri is trustworthy, one of the teachers of Ahmad. He settled in Makkah, and Ahmad heard from him there, as will come in 15057. Ahmad and Nasai both affirmed his reliability, and Bukhari mentioned him in Kabir 1/1/460. Abdullah is Ibn Umar Umari. This hadith is a repetition of 4919, and in full at 5657.