"I saw the Messenger of Allah ﷺ delivering the khutbah on Friday standing, then he sat briefly and did not speak, then he stood up and delivered a second khutbah. So whoever tells you that the Messenger of Allah ﷺ used to deliver the khutbah seated, he has lied." (Using translation from Nasāʾī 1417)
رَأَيْتُ رَسُولَ اللهِ ﷺ «يَخْطُبُ يَوْمَ الْجُمُعَةِ قَائِمًا ثُمَّ يَقْعُدَ قَعْدَةً لَا يَتَكَلَّمُ ثُمَّ يَقُومُ فَيَخْطُبُ خُطْبَةً أُخْرَى فَمَنْ حَدَّثَكُمْ أَنَّ رَسُولَ اللهِ ﷺ خَطَبَ قَاعِدًا فَقَدْ كَذَبَ»