Musannaf Ibn Abi Shayba 1:1788

Abu Khalid al-Ahmar narrated to us, from Hizam (or Haram) ibn Uthman, from Abu Atiq, from Jabir, who said: He used to use the siwak when he took to his bed, and when he rose at night, and when he went out for the morning prayer. He said: So I said to him, "You have burdened yourself with this siwak." He replied, "Indeed, Usama informed me that the Messenger of Allah, may Allah bless him and grant him peace, used to use the siwak in this manner."