Musnad Ahmad 1153:778

Aswad ibn Amir narrated to us, he said: Sharik narrated to us, from al-Miqdam ibn Shurayh, from his father, from Aisha, she said: "The first thing he would begin with when he entered his house was the siwak (tooth stick), and the last thing when he left his house was the two rak'ahs before the dawn."