"I saw the Messenger of Allah ﷺ delivering the Khutbah standing up, then he sat down for a while and did not speak, then he stood up and delivered another Khutbah. Whoever tells you that the Prophet ﷺ delivered a Khutbah sitting do not believe him." (Using translation from Nasāʾī 1583)
رَأَيْتُ رَسُولَ اللهِ ﷺ يَخْطُبُ قَائِمًا ثُمَّ يَقْعُدُ قَعْدَةً لَا يَتَكَلَّمُ ثُمَّ يَقُومُ يَخْطُبُ خُطْبَةً أُخْرَى عَلَى مِنْبَرِهِ فَمَنْ حَدَّثَكَ أَنَّهُ يَرَاهُ يَخْطُبُ قَاعِدًا فَلَا تُصَدِّقْهُ