It was narrated from ‘Amr bin Shu’aib, from his father, that his grandfather said:“The Messenger of Allah (ﷺ) forbade Ihtiba’ (sitting with one's thighs gathered up against the stomach while wrapping one's arm or garment around them) on Fridays, meaning, when the Imam is delivering the sermon.”
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُصَفَّى الْحِمْصِيُّ، حَدَّثَنَا بَقِيَّةُ، عَنْ عَبْدِ اللَّهِ بْنِ وَاقِدٍ، عَنْ مُحَمَّدِ بْنِ عَجْلاَنَ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ نَهَى رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ عَنْ الاِحْتِبَاءِ يَوْمَ الْجُمُعَةِ - يَعْنِي - وَالإِمَامُ يَخْطُبُ .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 1134