Musannaf Ibn Abi Shayba 3:454

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Zakariya, from al-Sha’bi, who said: Ibn Mas’ud entered upon his brother ‘Utbah while he was ill, and he was prostrating upon a *siwak*. So he threw it away and said: "Gesture with a gesture."