Musnad Ahmad 32:1465

Muhammad ibn Abdullah narrated to us, Humayd narrated to us, from Anas, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to come to the house of Umm Sulaym and sleep on her bed, while Umm Sulaym was not in her house. She would come and find him sleeping. When the Prophet (peace and blessings of Allah be upon him) slept, he would perspire. She would take his sweat with a piece of cotton and put it into a bottle, then she would put it into her perfume."