Musnad Ahmad 1153:1469

Yazid narrated to us, Sharik informed us, from al-Miqdam, from his father, who said: I said to Aisha, "O Mother, with what thing would the Messenger of Allah, peace and blessings of Allah be upon him, begin when he entered your house, and with what thing would he conclude?" She said: "He would begin with the siwak (tooth-stick), and he would conclude with the two rak'ahs of the dawn."