Musnad Ahmad 1153:207

Isma'il narrated to us, he said: Ayyub informed us, from Ibn Abi Mulaykah, who said: 'Aishah said: The Messenger of Allah (peace and blessings of Allah be upon him) died in my house, on my day, and between my chest and my throat. Then 'Abd al-Rahman ibn Abi Bakr entered, and with him was a moist siwak (tooth stick). He looked at it, and I thought that he had a need for it. She said: So I took it, chewed it, shook it out, and made it good. Then I handed it to him, and he used it to brush his teeth in the best manner I had ever seen him brush his teeth. Then he went to raise it toward me, but it fell from his hand. I began to supplicate to Allah (the Mighty and Majestic) with a supplication that Jibril (peace be upon him) used to supplicate for him with, and which he used to supplicate with when he was ill, but he did not supplicate with it during that illness of his. He raised his gaze toward the sky and said: "The Highest Companion, the Highest Companion." Meaning, his soul departed. So praise be to Allah, who joined my saliva with his saliva on the last day of the days of the world.