Musnad Ahmad 1153:1574

Waki' narrated to us, he said: Sufyan narrated to us, from al-Miqdam ibn Shurayh ibn Hani' al-Harithi, from his father, who said: I said to Aisha: "With what thing would the Messenger of Allah, peace and blessings of Allah be upon him, begin when he entered his house?" She said: "With the siwak."