Musnad Ahmad 1153:1979

Yazid narrated to us, he said: Sharik informed us, from al-Miqdam, from his father, who said: I said to Aisha: "O Mother, with what did the Prophet, may God bless him and grant him peace, begin when he entered your house? And with what did he conclude?" She said: "He would begin with the siwak (tooth stick), and he would conclude with the two rak'ahs of the dawn (prayer)."