It is narrated from Sayyidah Aishah (may Allah be pleased with her) that in the illness in which he (peace and blessings be upon him) passed away, the Prophet (peace and blessings be upon him) used to ask: "Where will I be tomorrow? Where will I be tomorrow?" He meant Sayyidah Aishah (may Allah be pleased with her), that is, her turn. So his (peace and blessings be upon him) wives gave permission that he (peace and blessings be upon him) could stay wherever he wished, and so his (peace and blessings be upon him) death took place in the house of Sayyidah Aishah (may Allah be pleased with her). Sayyidah Aishah (may Allah be pleased with her) said: He (peace and blessings be upon him) passed away on the day that was my turn; he (peace and blessings be upon him) was taken in my house, and his (peace and blessings be upon him) blessed head was between my chest and my chin, and his (peace and blessings be upon him) saliva mixed with mine. She said: Abd al-Rahman bin Abi Bakr came in with a tooth-stick (miswak) which he was using. He (peace and blessings be upon him) looked at it. I said: O Abd al-Rahman! Give me the miswak. I softened it, then chewed it, and gave it to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) used it while he (peace and blessings be upon him) was reclining against my chest.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13430