Sahih Muslim 1994
The Book of Prayer - Friday
وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ الْقَوَارِيرِيُّ، وَأَبُو كَامِلٍ الْجَحْدَرِيُّ جَمِيعًا عَنْ خَالِدٍ، - قَالَ أَبُو كَامِلٍ حَدَّثَنَا خَالِدُ بْنُ الْحَارِثِ، - حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَخْطُبُ يَوْمَ الْجُمُعَةِ قَائِمًا ثُمَّ يَجْلِسُ ثُمَّ يَقُومُ . قَالَ كَمَا يَفْعَلُونَ الْيَوْمَ .
Ibn 'Umar said that the Messenger of Allah (ﷺ) used to deliver the sermon on Friday while standing. He would then sit and then stand (for the second sermon) as they (the Muslims) do nowadays
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.