Musnad Ahmad 132:22

Abu Abd al-Rahman Abdullah ibn Yazid narrated to us, Sa'id ibn Abi Ayyub narrated to us, he said: Abu Marhum Abd al-Rahim ibn Maymun informed me, from Sahl ibn Mu'adh ibn Anas al-Juhani, from his father, from the Messenger of Allah, peace and blessings of Allah be upon him: "That he forbade the *habwah* (sitting with the knees drawn up to the chest) on the day of Jumu'ah while the Imam is delivering the sermon."