It is narrated from Sayyiduna Mu'adh bin Anas al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) forbade sitting in ihtiba' (sitting with the knees drawn up to the stomach and wrapped in a garment) on Friday while the imam is delivering the sermon.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17519