Musnad Abu Ya'la al-Mawsili 150:81

Ja'far ibn Mihran narrated to us, 'Abd al-A'la narrated to us, Muhammad ibn Ishaq narrated to us, Ya'qub ibn 'Utbah narrated to me, from al-Zuhri, from 'Urwah, from 'A'ishah, who said: The Messenger of Allah (may Allah bless him and grant him peace) returned and lay down in my room on that day when he entered from the mosque. A man from the family of Abu Bakr entered upon me, and in his hand was a green tooth-stick (siwak). She said: The Messenger of Allah (may Allah bless him and grant him peace) looked at it while it was in his hand with a look by which I knew that he wanted it. I said: "O Messenger of Allah, would you like for me to give you this tooth-stick?" He said: "Yes." So I took it and chewed it for him until I softened it, then I gave it to him. She said: So he cleaned his teeth with it in the best manner I had ever seen him clean his teeth with a tooth-stick before that. She said: Then he put it down, and I found the Messenger of Allah (may Allah bless him and grant him peace) becoming heavy in my lap. She said: I went to look at his face, and his gaze had become fixed, and he was saying: "Rather, the Highest Companion from Paradise." She said: So I said: "You were given a choice, and you chose. By the One who sent you with the truth." She said: And the Messenger of Allah (may Allah bless him and grant him peace) passed away.